Support do-while where test is negative.

reference/shaders-no-opt/asm/frag/do-while-loop-inverted-test.asm.frag

@@ -0,0 +1,13 @@
+#version 450
+
+void main()
+{
+    int j = 0;
+    int i = 0;
+    do
+    {
+        j = ((j + i) + 1) * j;
+        i++;
+    } while (!(i == 20));
+}
+

reference/shaders-no-opt/asm/frag/for-loop-dedicated-merge-block-inverted.asm.frag

@@ -0,0 +1,11 @@
+#version 450
+
+void main()
+{
+    int _13;
+    for (int _12 = 0; !(_12 == 16); _12 = _13)
+    {
+        _13 = _12 + 1;
+    }
+}
+

reference/shaders-no-opt/asm/frag/for-loop-dedicated-merge-block-non-inverted.asm.frag

@@ -0,0 +1,11 @@
+#version 450
+
+void main()
+{
+    int _13;
+    for (int _12 = 0; _12 != 16; _12 = _13)
+    {
+        _13 = _12 + 1;
+    }
+}
+

reference/shaders-no-opt/asm/frag/for-loop-inverted-test.asm.frag

@@ -0,0 +1,11 @@
+#version 450
+
+void main()
+{
+    int _13;
+    for (int _12 = 0; !(_12 == 16); _12 = _13)
+    {
+        _13 = _12 + 1;
+    }
+}
+

reference/shaders-no-opt/asm/frag/while-loop-inverted-test.asm.frag

@@ -0,0 +1,13 @@
+#version 450
+
+void main()
+{
+    int i = 0;
+    int j = 0;
+    while (!(i == 20))
+    {
+        j = ((j + i) + 1) * j;
+        i++;
+    }
+}
+

shaders-no-opt/asm/frag/do-while-loop-inverted-test.asm.frag

@@ -0,0 +1,51 @@
+; SPIR-V
+; Version: 1.0
+; Generator: Khronos Glslang Reference Front End; 7
+; Bound: 28
+; Schema: 0
+               OpCapability Shader
+          %1 = OpExtInstImport "GLSL.std.450"
+               OpMemoryModel Logical GLSL450
+               OpEntryPoint Fragment %main "main"
+               OpExecutionMode %main OriginUpperLeft
+               OpSource GLSL 450
+               OpName %main "main"
+               OpName %i "i"
+               OpName %j "j"
+       %void = OpTypeVoid
+          %3 = OpTypeFunction %void
+        %int = OpTypeInt 32 1
+%_ptr_Function_int = OpTypePointer Function %int
+      %int_0 = OpConstant %int 0
+      %int_1 = OpConstant %int 1
+     %int_20 = OpConstant %int 20
+       %bool = OpTypeBool
+       %main = OpFunction %void None %3
+          %5 = OpLabel
+          %i = OpVariable %_ptr_Function_int Function
+          %j = OpVariable %_ptr_Function_int Function
+               OpStore %i %int_0
+               OpStore %j %int_0
+               OpBranch %11
+         %11 = OpLabel
+               OpLoopMerge %13 %14 None
+               OpBranch %12
+         %12 = OpLabel
+         %15 = OpLoad %int %j
+         %16 = OpLoad %int %i
+         %17 = OpIAdd %int %15 %16
+         %19 = OpIAdd %int %17 %int_1
+         %20 = OpLoad %int %j
+         %21 = OpIMul %int %19 %20
+               OpStore %j %21
+         %22 = OpLoad %int %i
+         %23 = OpIAdd %int %22 %int_1
+               OpStore %i %23
+               OpBranch %14
+         %14 = OpLabel
+         %24 = OpLoad %int %i
+         %27 = OpIEqual %bool %24 %int_20
+               OpBranchConditional %27 %13 %11
+         %13 = OpLabel
+               OpReturn
+               OpFunctionEnd

shaders-no-opt/asm/frag/for-loop-dedicated-merge-block-inverted.asm.frag

@@ -0,0 +1,37 @@
+               OpCapability Shader
+          %1 = OpExtInstImport "GLSL.std.450"
+               OpMemoryModel Logical GLSL450
+               OpEntryPoint Fragment %main "main"
+               OpExecutionMode %main OriginUpperLeft
+               OpSource GLSL 450
+               OpName %main "main"
+       %void = OpTypeVoid
+          %3 = OpTypeFunction %void
+        %int = OpTypeInt 32 1
+      %int_0 = OpConstant %int 0
+     %int_16 = OpConstant %int 16
+       %bool = OpTypeBool
+      %int_1 = OpConstant %int 1
+       %main = OpFunction %void None %3
+          %5 = OpLabel
+               OpBranch %8
+          %8 = OpLabel
+         %10 = OpPhi %int %12 %7 %int_0 %5
+               OpLoopMerge %6 %7 None
+               OpBranch %11
+         %11 = OpLabel
+         %16 = OpIEqual %bool %10 %int_16
+               OpBranchConditional %16 %18 %19
+         %18 = OpLabel
+               OpBranch %6
+         %19 = OpLabel
+               OpBranch %17
+         %17 = OpLabel
+         %21 = OpIAdd %int %10 %int_1
+               OpBranch %7
+          %7 = OpLabel
+         %12 = OpPhi %int %21 %17
+               OpBranch %8
+          %6 = OpLabel
+               OpReturn
+               OpFunctionEnd

shaders-no-opt/asm/frag/for-loop-dedicated-merge-block-non-inverted.asm.frag

@@ -0,0 +1,37 @@
+               OpCapability Shader
+          %1 = OpExtInstImport "GLSL.std.450"
+               OpMemoryModel Logical GLSL450
+               OpEntryPoint Fragment %main "main"
+               OpExecutionMode %main OriginUpperLeft
+               OpSource GLSL 450
+               OpName %main "main"
+       %void = OpTypeVoid
+          %3 = OpTypeFunction %void
+        %int = OpTypeInt 32 1
+      %int_0 = OpConstant %int 0
+     %int_16 = OpConstant %int 16
+       %bool = OpTypeBool
+      %int_1 = OpConstant %int 1
+       %main = OpFunction %void None %3
+          %5 = OpLabel
+               OpBranch %8
+          %8 = OpLabel
+         %10 = OpPhi %int %12 %7 %int_0 %5
+               OpLoopMerge %6 %7 None
+               OpBranch %11
+         %11 = OpLabel
+         %16 = OpINotEqual %bool %10 %int_16
+               OpBranchConditional %16 %19 %18
+         %18 = OpLabel
+               OpBranch %6
+         %19 = OpLabel
+               OpBranch %17
+         %17 = OpLabel
+         %21 = OpIAdd %int %10 %int_1
+               OpBranch %7
+          %7 = OpLabel
+         %12 = OpPhi %int %21 %17
+               OpBranch %8
+          %6 = OpLabel
+               OpReturn
+               OpFunctionEnd

shaders-no-opt/asm/frag/for-loop-inverted-test.asm.frag

@@ -0,0 +1,35 @@
+               OpCapability Shader
+          %1 = OpExtInstImport "GLSL.std.450"
+               OpMemoryModel Logical GLSL450
+               OpEntryPoint Fragment %main "main"
+               OpExecutionMode %main OriginUpperLeft
+               OpSource GLSL 450
+               OpName %main "main"
+       %void = OpTypeVoid
+          %3 = OpTypeFunction %void
+        %int = OpTypeInt 32 1
+      %int_0 = OpConstant %int 0
+     %int_16 = OpConstant %int 16
+       %bool = OpTypeBool
+      %int_1 = OpConstant %int 1
+       %main = OpFunction %void None %3
+          %5 = OpLabel
+               OpBranch %8
+          %8 = OpLabel
+         %10 = OpPhi %int %12 %7 %int_0 %5
+               OpLoopMerge %6 %7 None
+               OpBranch %11
+         %11 = OpLabel
+         %16 = OpIEqual %bool %10 %int_16
+               OpBranchConditional %16 %6 %19
+         %19 = OpLabel
+               OpBranch %17
+         %17 = OpLabel
+         %21 = OpIAdd %int %10 %int_1
+               OpBranch %7
+          %7 = OpLabel
+         %12 = OpPhi %int %21 %17
+               OpBranch %8
+          %6 = OpLabel
+               OpReturn
+               OpFunctionEnd

shaders-no-opt/asm/frag/while-loop-inverted-test.asm.frag

@@ -0,0 +1,53 @@
+; SPIR-V
+; Version: 1.0
+; Generator: Khronos Glslang Reference Front End; 7
+; Bound: 29
+; Schema: 0
+               OpCapability Shader
+          %1 = OpExtInstImport "GLSL.std.450"
+               OpMemoryModel Logical GLSL450
+               OpEntryPoint Fragment %main "main"
+               OpExecutionMode %main OriginUpperLeft
+               OpSource GLSL 450
+               OpName %main "main"
+               OpName %i "i"
+               OpName %j "j"
+       %void = OpTypeVoid
+          %3 = OpTypeFunction %void
+        %int = OpTypeInt 32 1
+%_ptr_Function_int = OpTypePointer Function %int
+      %int_0 = OpConstant %int 0
+     %int_20 = OpConstant %int 20
+       %bool = OpTypeBool
+      %int_1 = OpConstant %int 1
+       %main = OpFunction %void None %3
+          %5 = OpLabel
+          %i = OpVariable %_ptr_Function_int Function
+          %j = OpVariable %_ptr_Function_int Function
+               OpStore %i %int_0
+               OpStore %j %int_0
+               OpBranch %11
+         %11 = OpLabel
+               OpLoopMerge %13 %14 None
+               OpBranch %15
+         %15 = OpLabel
+         %16 = OpLoad %int %i
+         %19 = OpIEqual %bool %16 %int_20
+               OpBranchConditional %19 %13 %12
+         %12 = OpLabel
+         %20 = OpLoad %int %j
+         %21 = OpLoad %int %i
+         %22 = OpIAdd %int %20 %21
+         %24 = OpIAdd %int %22 %int_1
+         %25 = OpLoad %int %j
+         %26 = OpIMul %int %24 %25
+               OpStore %j %26
+         %27 = OpLoad %int %i
+         %28 = OpIAdd %int %27 %int_1
+               OpStore %i %28
+               OpBranch %14
+         %14 = OpLabel
+               OpBranch %11
+         %13 = OpLabel
+               OpReturn
+               OpFunctionEnd

spirv_cross.cpp

@@ -1611,8 +1611,20 @@ SPIRBlock::ContinueBlockType Compiler::continue_block_type(const SPIRBlock &bloc
 		return SPIRBlock::ForLoop;
 	else
 	{
+		const auto *false_block = maybe_get<SPIRBlock>(block.false_block);
+		const auto *true_block = maybe_get<SPIRBlock>(block.true_block);
+		const auto *merge_block = maybe_get<SPIRBlock>(dominator.merge_block);
+
+		bool positive_do_while = block.true_block == dominator.self &&
+		                         (block.false_block == dominator.merge_block ||
+		                          (false_block && merge_block && execution_is_noop(*false_block, *merge_block)));
+
+		bool negative_do_while = block.false_block == dominator.self &&
+		                         (block.true_block == dominator.merge_block ||
+		                          (true_block && merge_block && execution_is_noop(*true_block, *merge_block)));
+
 		if (block.merge == SPIRBlock::MergeNone && block.terminator == SPIRBlock::Select &&
-		    block.true_block == dominator.self && block.false_block == dominator.merge_block)
+		    (positive_do_while || negative_do_while))
 		{
 			return SPIRBlock::DoWhileLoop;
 		}

spirv_glsl.cpp

@@ -10205,7 +10205,7 @@ void CompilerGLSL::propagate_loop_dominators(const SPIRBlock &block)
 // FIXME: This currently cannot handle complex continue blocks
 // as in do-while.
 // This should be seen as a "trivial" continue block.
-string CompilerGLSL::emit_continue_block(uint32_t continue_block)
+string CompilerGLSL::emit_continue_block(uint32_t continue_block, bool follow_true_block, bool follow_false_block)
 {
 	auto *block = &get<SPIRBlock>(continue_block);
 
@@ -10233,11 +10233,20 @@ string CompilerGLSL::emit_continue_block(uint32_t continue_block)
 			block = &get<SPIRBlock>(block->next_block);
 		}
 		// For do while blocks. The last block will be a select block.
-		else if (block->true_block)
+		else if (block->true_block && follow_true_block)
 		{
 			flush_phi(continue_block, block->true_block);
 			block = &get<SPIRBlock>(block->true_block);
 		}
+		else if (block->false_block && follow_false_block)
+		{
+			flush_phi(continue_block, block->false_block);
+			block = &get<SPIRBlock>(block->false_block);
+		}
+		else
+		{
+			SPIRV_CROSS_THROW("Invalid continue block detected!");
+		}
 	}
 
 	// Restore old pointer.
@@ -10400,7 +10409,7 @@ bool CompilerGLSL::attempt_emit_loop_header(SPIRBlock &block, SPIRBlock::Method
 				emit_block_hints(block);
 				if (method != SPIRBlock::MergeToSelectContinueForLoop)
 				{
-					auto continue_block = emit_continue_block(block.continue_block);
+					auto continue_block = emit_continue_block(block.continue_block, false, false);
 					statement("for (", initializer, "; ", condition, "; ", continue_block, ")");
 				}
 				else
@@ -10476,7 +10485,7 @@ bool CompilerGLSL::attempt_emit_loop_header(SPIRBlock &block, SPIRBlock::Method
 					target_block = child.false_block;
 				}
 
-				auto continue_block = emit_continue_block(block.continue_block);
+				auto continue_block = emit_continue_block(block.continue_block, false, false);
 				emit_block_hints(block);
 				statement("for (", initializer, "; ", condition, "; ", continue_block, ")");
 				break;
@@ -10617,6 +10626,7 @@ void CompilerGLSL::emit_block_chain(SPIRBlock &block)
 	{
 		flush_undeclared_variables(block);
 		emit_while_loop_initializers(block);
+		emitted_for_loop_header = true;
 		// We have some temporaries where the loop header is the dominator.
 		// We risk a case where we have code like:
 		// for (;;) { create-temporary; break; } consume-temporary;
@@ -10908,7 +10918,12 @@ void CompilerGLSL::emit_block_chain(SPIRBlock &block)
 			// Make sure that we run the continue block to get the expressions set, but this
 			// should become an empty string.
 			// We have no fallbacks if we cannot forward everything to temporaries ...
-			auto statements = emit_continue_block(block.continue_block);
+			const auto &continue_block = get<SPIRBlock>(block.continue_block);
+			bool positive_test =
+					execution_is_noop(get<SPIRBlock>(continue_block.true_block),
+					                  get<SPIRBlock>(continue_block.loop_dominator));
+
+			auto statements = emit_continue_block(block.continue_block, positive_test, !positive_test);
 			if (!statements.empty())
 			{
 				// The DoWhile block has side effects, force ComplexLoop pattern next pass.
@@ -10916,7 +10931,12 @@ void CompilerGLSL::emit_block_chain(SPIRBlock &block)
 				force_recompile = true;
 			}
 
-			end_scope_decl(join("while (", to_expression(get<SPIRBlock>(block.continue_block).condition), ")"));
+			// Might have to invert the do-while test here.
+			auto condition = to_expression(continue_block.condition);
+			if (!positive_test)
+				condition = join("!", enclose_expression(condition));
+
+			end_scope_decl(join("while (", condition, ")"));
 		}
 		else
 			end_scope();

spirv_glsl.hpp

@@ -403,7 +403,7 @@ protected:
 	std::string constant_value_macro_name(uint32_t id);
 	void emit_constant(const SPIRConstant &constant);
 	void emit_specialization_constant_op(const SPIRConstantOp &constant);
-	std::string emit_continue_block(uint32_t continue_block);
+	std::string emit_continue_block(uint32_t continue_block, bool follow_true_block, bool follow_false_block);
 	bool attempt_emit_loop_header(SPIRBlock &block, SPIRBlock::Method method);
 	void propagate_loop_dominators(const SPIRBlock &block);