Add unit tests for for-loop unrolling

Change-Id: I350a6768ac124362b0d3e0f17e7a026265acf804
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/353627
Reviewed-by: Mike Klein <mtklein@google.com>
Commit-Queue: Brian Osman <brianosman@google.com>

gn/sksl_tests.gni

@@ -485,6 +485,8 @@ sksl_settings_tests = [
 
 sksl_rte_tests = [
   "$_tests/sksl/runtime/ConversionConstructors.rte",
+  "$_tests/sksl/runtime/LoopInt.rte",
+  "$_tests/sksl/runtime/LoopFloat.rte",
   "$_tests/sksl/runtime/SampleWithConstantMatrix.rte",
   "$_tests/sksl/runtime/SampleWithExplicitCoord.rte",
   "$_tests/sksl/runtime/SampleWithUniformMatrix.rte",

src/core/SkVM.cpp

@@ -920,16 +920,20 @@ namespace skvm {
 
     I32 Builder:: eq(I32 x, I32 y) {
         if (x.id == y.id) { return splat(~0); }
+        if (int X,Y; this->allImm(x.id,&X, y.id,&Y)) { return splat(X==Y ? ~0 : 0); }
         return {this, this->push(Op:: eq_i32, x.id, y.id)};
     }
     I32 Builder::neq(I32 x, I32 y) {
+        if (int X,Y; this->allImm(x.id,&X, y.id,&Y)) { return splat(X!=Y ? ~0 : 0); }
         return ~(x == y);
     }
     I32 Builder:: gt(I32 x, I32 y) {
+        if (int X,Y; this->allImm(x.id,&X, y.id,&Y)) { return splat(X> Y ? ~0 : 0); }
         return {this, this->push(Op:: gt_i32, x.id, y.id)};
     }
     I32 Builder::gte(I32 x, I32 y) {
         if (x.id == y.id) { return splat(~0); }
+        if (int X,Y; this->allImm(x.id,&X, y.id,&Y)) { return splat(X>=Y ? ~0 : 0); }
         return ~(x < y);
     }
     I32 Builder:: lt(I32 x, I32 y) { return y>x; }

tests/sksl/runtime/LoopFloat.rte

@@ -0,0 +1,40 @@
+// Should return 5
+float return_loop() {
+    for (float i = 0; i < 10; ++i) {
+        if (i == 5) { return i; }
+    }
+    return 0;
+}
+
+// Should return 35
+float continue_loop() {
+    float sum = 0;
+    for (float i = 0; i < 10; ++i) {
+        if (i < 5) { continue; }
+        sum += i;
+    }
+    return sum;
+}
+
+// Should return 15
+float break_loop() {
+    float sum = 0;
+    for (float i = 0; i < 10; ++i) {
+        if (i > 5) { break; }
+        sum += i;
+    }
+    return sum;
+}
+
+// Should return ~1.725
+float float_loop() {
+    float sum = 0;
+    for (float i = 0.123; i < 0.6; i += 0.111) {
+        sum += i;
+    }
+    return sum;
+}
+
+half4 main() {
+    return half4(return_loop(), continue_loop(), break_loop(), float_loop());
+}

tests/sksl/runtime/LoopInt.rte

@@ -0,0 +1,31 @@
+// Should return 5
+int return_loop() {
+    for (int i = 0; i < 10; ++i) {
+        if (i == 5) { return i; }
+    }
+    return 0;
+}
+
+// Should return 35
+int continue_loop() {
+    int sum = 0;
+    for (int i = 0; i < 10; ++i) {
+        if (i < 5) { continue; }
+        sum += i;
+    }
+    return sum;
+}
+
+// Should return 15
+int break_loop() {
+    int sum = 0;
+    for (int i = 0; i < 10; ++i) {
+        if (i > 5) { break; }
+        sum += i;
+    }
+    return sum;
+}
+
+half4 main() {
+    return half4(return_loop(), continue_loop(), break_loop(), 1);
+}

tests/sksl/runtime/golden/LoopFloat.skvm

@@ -0,0 +1,10 @@
+4 registers, 8 instructions:
+0	r0 = splat 40A00000 (5)
+1	r1 = splat 420C0000 (35)
+2	r2 = splat 41700000 (15)
+3	r3 = splat 3FDCCCCD (1.725)
+loop:
+4	    store32 ptr1 r0
+5	    store32 ptr2 r1
+6	    store32 ptr3 r2
+7	    store32 ptr4 r3

tests/sksl/runtime/golden/LoopInt.skvm

@@ -0,0 +1,10 @@
+4 registers, 8 instructions:
+0	r0 = splat 40A00000 (5)
+1	r1 = splat 420C0000 (35)
+2	r2 = splat 41700000 (15)
+3	r3 = splat 3F800000 (1)
+loop:
+4	    store32 ptr1 r0
+5	    store32 ptr2 r1
+6	    store32 ptr3 r2
+7	    store32 ptr4 r3