[spirv] set needsLegalization as true when variable offset is found (#3820)

When we find a variable offset used for the texture sampling, we have to
- Run legalization if `-fcgl` is not enabled.
- Enable `--before-legalize-hlsl` for spirv-val if `-fcgl` is enabled.
to match the behavior of the DXIL backend.

In order to do that, we set SpirvEmitter::needsLegalization as true when
we find a variable offset used for the texture sampling. SpirvEmitter
will determine enabling `--before-legalize-hlsl` or running the
legalization depending on `-fcgl`.

Author: jaebaek

tools/clang/lib/SPIRV/SpirvEmitter.cpp

@@ -4461,6 +4461,9 @@ SpirvInstruction *SpirvEmitter::createImageSample(
     SpirvInstruction *minLod, SpirvInstruction *residencyCodeId,
     SourceLocation loc) {
 
+  if (varOffset)
+    needsLegalization = true;
+
   // SampleDref* instructions in SPIR-V always return a scalar.
   // They also have the correct type in HLSL.
   if (compareVal) {
@@ -4893,6 +4896,9 @@ SpirvEmitter::processBufferTextureLoad(const CXXMemberCallExpr *expr) {
         handleOffsetInMethodCall(expr, 1, &constOffset, &varOffset);
     }
 
+    if (varOffset)
+      needsLegalization = true;
+
     return processBufferTextureLoad(object, coordinate, constOffset, varOffset,
                                     lod, status, loc);
   }

tools/clang/test/CodeGenSPIRV/texture.sample.offset.needs.legalization.hlsl

@@ -0,0 +1,25 @@
+// Run: %dxc -T ps_6_0 -E main
+
+SamplerState      gSampler  : register(s5);
+Texture2D<float4> t         : register(t1);
+
+// This shader uses a variable offset for texture sampling that is supposed to
+// be converted to a constant value after the legalization. Since we set
+// needsLegalization as true when we find a variable offset for texture
+// sampling, `--before-legalize-hlsl` option for spirv-val should be enabled
+// because of `-fcgl`.
+
+// CHECK:      OpImageSparseSampleImplicitLod
+// CHECK-SAME: Offset
+
+float4 sample(int offset, float clamp) {
+    uint status;
+    return t.Sample(gSampler, float2(0.1, 0.2), offset, clamp, status);
+}
+
+float4 main(int2 offset: A) : SV_Target {
+    float4 val = 0;
+    [unroll] for (int i = 0; i < 3; ++i)
+        val = sample(i, offset.x);
+    return val;
+}

tools/clang/test/CodeGenSPIRV/texture.sample.offset.needs.legalization.o0.hlsl

@@ -0,0 +1,22 @@
+// Run: %dxc -T ps_6_0 -E main -O0
+
+SamplerState      gSampler  : register(s5);
+Texture2D<float4> t         : register(t1);
+
+// This shader uses a variable offset for texture sampling that is supposed to
+// be converted to a constant value after the legalization.
+
+// CHECK:      OpImageSparseSampleImplicitLod
+// CHECK-SAME: ConstOffset
+
+float4 sample(int offset, float clamp) {
+    uint status;
+    return t.Sample(gSampler, float2(0.1, 0.2), offset, clamp, status);
+}
+
+float4 main(int2 offset: A) : SV_Target {
+    float4 val = 0;
+    [unroll] for (int i = 0; i < 3; ++i)
+        val = sample(i, offset.x);
+    return val;
+}

tools/clang/test/CodeGenSPIRV/texture.sample.variable-offset.hlsl

@@ -0,0 +1,23 @@
+// Run: %dxc -T ps_6_0 -E main
+SamplerState      gSampler  : register(s5);
+Texture2D<float4> t         : register(t1);
+
+// This shader uses a variable offset for texture sampling, which is illegal.
+// Since we set needsLegalization as true when we find a variable offset for
+// texture sampling, `--before-legalize-hlsl` option for spirv-val should be
+// enabled because of `-fcgl`. Therefore, it must not generate any errors.
+
+// CHECK:      OpImageSparseSampleImplicitLod
+// CHECK-SAME: Offset
+
+float4 sample(int2 offset, float clamp) {
+    uint status;
+    return t.Sample(gSampler, float2(0.1, 0.2), offset, clamp, status);
+}
+
+float4 main(int2 offset: A) : SV_Target {
+    float4 val = 0;
+    for (int i = 0; i < 3; ++i)
+        val = sample(offset, i);
+    return val;
+}

tools/clang/unittests/SPIRV/CodeGenSpirvTest.cpp

@@ -980,6 +980,17 @@ TEST_F(FileTest, TextureInvalidTex2D) {
 TEST_F(FileTest, TextureSampleOffsetWithLoopUnroll) {
   runFileTest("texture.sample-offset.with.loop-unroll.hlsl");
 }
+TEST_F(FileTest, TextureSampleVariableOffsetBeforeLegalizeHLSL) {
+  setBeforeHLSLLegalization();
+  runFileTest("texture.sample.variable-offset.hlsl");
+}
+TEST_F(FileTest, TextureSampleOffsetNeedsLegalization) {
+  setBeforeHLSLLegalization();
+  runFileTest("texture.sample.offset.needs.legalization.hlsl");
+}
+TEST_F(FileTest, TextureSampleConstOffsetAfterLegalization) {
+  runFileTest("texture.sample.offset.needs.legalization.o0.hlsl");
+}
 
 // For structured buffer methods
 TEST_F(FileTest, StructuredBufferLoad) {