Fall back to complex loop if non-trivial continue block is found.

There is a case where we can deduce a for/while loop, but the continue
block is actually very painful to deal with, so handle that case as
well. Removes an exceptional case.

reference/opt/shaders-hlsl/frag/for-loop-continue-control-flow.frag

@@ -0,0 +1,25 @@
+static float4 FragColor;
+
+struct SPIRV_Cross_Output
+{
+    float4 FragColor : SV_Target0;
+};
+
+void frag_main()
+{
+    FragColor = 0.0f.xxxx;
+    for (int _43 = 0; _43 < 3; )
+    {
+        FragColor[_43] += float(_43);
+        _43++;
+        continue;
+    }
+}
+
+SPIRV_Cross_Output main()
+{
+    frag_main();
+    SPIRV_Cross_Output stage_output;
+    stage_output.FragColor = FragColor;
+    return stage_output;
+}

reference/opt/shaders-msl/frag/for-loop-continue-control-flow.frag

@@ -0,0 +1,23 @@
+#include <metal_stdlib>
+#include <simd/simd.h>
+
+using namespace metal;
+
+struct main0_out
+{
+    float4 FragColor [[color(0)]];
+};
+
+fragment main0_out main0()
+{
+    main0_out out = {};
+    out.FragColor = float4(0.0);
+    for (int _43 = 0; _43 < 3; )
+    {
+        out.FragColor[_43] += float(_43);
+        _43++;
+        continue;
+    }
+    return out;
+}
+

reference/opt/shaders/frag/for-loop-continue-control-flow.frag

@@ -0,0 +1,15 @@
+#version 450
+
+layout(location = 0) out vec4 FragColor;
+
+void main()
+{
+    FragColor = vec4(0.0);
+    for (int _43 = 0; _43 < 3; )
+    {
+        FragColor[_43] += float(_43);
+        _43++;
+        continue;
+    }
+}
+

reference/shaders-hlsl/frag/for-loop-continue-control-flow.frag

@@ -0,0 +1,44 @@
+static float4 FragColor;
+
+struct SPIRV_Cross_Output
+{
+    float4 FragColor : SV_Target0;
+};
+
+void frag_main()
+{
+    FragColor = 0.0f.xxxx;
+    int i = 0;
+    int _36;
+    for (;;)
+    {
+        if (i < 3)
+        {
+            int a = i;
+            FragColor[a] += float(i);
+            if (false)
+            {
+                _36 = 1;
+            }
+            else
+            {
+                int _41 = i;
+                i = _41 + 1;
+                _36 = _41;
+            }
+            continue;
+        }
+        else
+        {
+            break;
+        }
+    }
+}
+
+SPIRV_Cross_Output main()
+{
+    frag_main();
+    SPIRV_Cross_Output stage_output;
+    stage_output.FragColor = FragColor;
+    return stage_output;
+}

reference/shaders-msl/frag/for-loop-continue-control-flow.frag

@@ -0,0 +1,42 @@
+#include <metal_stdlib>
+#include <simd/simd.h>
+
+using namespace metal;
+
+struct main0_out
+{
+    float4 FragColor [[color(0)]];
+};
+
+fragment main0_out main0()
+{
+    main0_out out = {};
+    out.FragColor = float4(0.0);
+    int i = 0;
+    int _36;
+    for (;;)
+    {
+        if (i < 3)
+        {
+            int a = i;
+            out.FragColor[a] += float(i);
+            if (false)
+            {
+                _36 = 1;
+            }
+            else
+            {
+                int _41 = i;
+                i = _41 + 1;
+                _36 = _41;
+            }
+            continue;
+        }
+        else
+        {
+            break;
+        }
+    }
+    return out;
+}
+

reference/shaders/frag/for-loop-continue-control-flow.frag

@@ -0,0 +1,34 @@
+#version 450
+
+layout(location = 0) out vec4 FragColor;
+
+void main()
+{
+    FragColor = vec4(0.0);
+    int i = 0;
+    int _36;
+    for (;;)
+    {
+        if (i < 3)
+        {
+            int a = i;
+            FragColor[a] += float(i);
+            if (false)
+            {
+                _36 = 1;
+            }
+            else
+            {
+                int _41 = i;
+                i = _41 + 1;
+                _36 = _41;
+            }
+            continue;
+        }
+        else
+        {
+            break;
+        }
+    }
+}
+

shaders-hlsl/frag/for-loop-continue-control-flow.frag

@@ -0,0 +1,11 @@
+#version 450
+layout(location = 0) out vec4 FragColor;
+void main()
+{
+	FragColor = vec4(0.0);
+	for (int i = 0; i < 3; (0 > 1) ? 1 : i ++)
+	{
+		int a = i;
+		FragColor[a] += float(i);
+	}
+}

shaders-msl/frag/for-loop-continue-control-flow.frag

@@ -0,0 +1,11 @@
+#version 450
+layout(location = 0) out vec4 FragColor;
+void main()
+{
+	FragColor = vec4(0.0);
+	for (int i = 0; i < 3; (0 > 1) ? 1 : i ++)
+	{
+		int a = i;
+		FragColor[a] += float(i);
+	}
+}

shaders/frag/for-loop-continue-control-flow.frag

@@ -0,0 +1,11 @@
+#version 450
+layout(location = 0) out vec4 FragColor;
+void main()
+{
+	FragColor = vec4(0.0);
+	for (int i = 0; i < 3; (0 > 1) ? 1 : i ++)
+	{
+		int a = i;
+		FragColor[a] += float(i);
+	}
+}

spirv_glsl.cpp

@@ -11226,7 +11226,10 @@ bool CompilerGLSL::attempt_emit_loop_header(SPIRBlock &block, SPIRBlock::Method
 			}
 
 			default:
-				SPIRV_CROSS_THROW("For/while loop detected, but need while/for loop semantics.");
+				block.disable_block_optimization = true;
+				force_recompile();
+				begin_scope(); // We'll see an end_scope() later.
+				return false;
 			}
 
 			begin_scope();
@@ -11300,7 +11303,10 @@ bool CompilerGLSL::attempt_emit_loop_header(SPIRBlock &block, SPIRBlock::Method
 			}
 
 			default:
-				SPIRV_CROSS_THROW("For/while loop detected, but need while/for loop semantics.");
+				block.disable_block_optimization = true;
+				force_recompile();
+				begin_scope(); // We'll see an end_scope() later.
+				return false;
 			}
 
 			begin_scope();