[SPIR-V] Fix OpVectorShuffle operands on load

The generated OpVectorShuffle was wrong, as the indices we pass are
not to select the vector to sample from, but the position in the vector.

Author: Keenuts

llvm/lib/Target/SPIRV/SPIRVLegalizePointerCast.cpp

@@ -81,8 +81,9 @@ class SPIRVLegalizePointerCast : public FunctionPass {
     LoadInst *NewLoad = B.CreateLoad(SourceType, Source);
     buildAssignType(B, SourceType, NewLoad);
 
-    SmallVector<int> Mask(/* Size= */ TargetType->getNumElements(),
-                          /* Value= */ 0);
+    SmallVector<int> Mask(/* Size= */ TargetType->getNumElements());
+    for (unsigned I = 0; I < TargetType->getNumElements(); ++I)
+      Mask[I] = I;
     Value *Output = B.CreateShuffleVector(NewLoad, NewLoad, Mask);
     buildAssignType(B, TargetType, Output);
     return Output;

llvm/test/CodeGen/SPIRV/pointers/getelementptr-downcast-vector.ll

@@ -19,7 +19,7 @@ define internal spir_func <3 x i32> @foo(ptr addrspace(10) %a) {
   ; partial loading of a vector: v4 -> v3.
   %2 = load <3 x i32>, ptr addrspace(10) %1, align 16
 ; CHECK: %[[#load:]] = OpLoad %[[#v4]] %[[#tmp]] Aligned 16
-; CHECK: %[[#val:]] = OpVectorShuffle %[[#v3]] %[[#load]] %[[#load]] 0 0 0
+; CHECK: %[[#val:]] = OpVectorShuffle %[[#v3]] %[[#load]] %[[#load]] 0 1 2
 
   ret <3 x i32> %2
 ; CHECK: OpReturnValue %[[#val]]
@@ -33,7 +33,7 @@ define internal spir_func <3 x i32> @fooDefault(ptr %a) {
   ; partial loading of a vector: v4 -> v3.
   %2 = load <3 x i32>, ptr %1, align 16
 ; CHECK: %[[#load:]] = OpLoad %[[#v4]] %[[#tmp]] Aligned 16
-; CHECK: %[[#val:]] = OpVectorShuffle %[[#v3]] %[[#load]] %[[#load]] 0 0 0
+; CHECK: %[[#val:]] = OpVectorShuffle %[[#v3]] %[[#load]] %[[#load]] 0 1 2
 
   ret <3 x i32> %2
 ; CHECK: OpReturnValue %[[#val]]
@@ -47,7 +47,7 @@ define internal spir_func <3 x i32> @fooBounds(ptr %a) {
   ; partial loading of a vector: v4 -> v3.
   %2 = load <3 x i32>, ptr %1, align 16
 ; CHECK: %[[#load:]] = OpLoad %[[#v4]] %[[#tmp]] Aligned 16
-; CHECK: %[[#val:]] = OpVectorShuffle %[[#v3]] %[[#load]] %[[#load]] 0 0 0
+; CHECK: %[[#val:]] = OpVectorShuffle %[[#v3]] %[[#load]] %[[#load]] 0 1 2
 
   ret <3 x i32> %2
 ; CHECK: OpReturnValue %[[#val]]
@@ -61,7 +61,7 @@ define internal spir_func <2 x i32> @bar(ptr addrspace(10) %a) {
   ; partial loading of a vector: v4 -> v2.
   %2 = load <2 x i32>, ptr addrspace(10) %1, align 16
 ; CHECK: %[[#load:]] = OpLoad %[[#v4]] %[[#tmp]] Aligned 16
-; CHECK: %[[#val:]] = OpVectorShuffle %[[#v2]] %[[#load]] %[[#load]] 0 0
+; CHECK: %[[#val:]] = OpVectorShuffle %[[#v2]] %[[#load]] %[[#load]] 0 1
 
   ret <2 x i32> %2
 ; CHECK: OpReturnValue %[[#val]]