[llvm] [SPIR-V] Fix OpVectorShuffle operands on load (PR #135954)

[Nathan Gauër via llvm-commits]

https://github.com/Keenuts updated https://github.com/llvm/llvm-project/pull/135954

>From dbeaab9df41c87a092b691fd46ae25bb86e83ce2 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Nathan=20Gau=C3=ABr?= <brioche at google.com>
Date: Wed, 16 Apr 2025 13:58:34 +0200
Subject: [PATCH] [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.
---
 llvm/lib/Target/SPIRV/SPIRVLegalizePointerCast.cpp        | 5 +++--
 .../SPIRV/pointers/getelementptr-downcast-vector.ll       | 8 ++++----
 2 files changed, 7 insertions(+), 6 deletions(-)

diff --git a/llvm/lib/Target/SPIRV/SPIRVLegalizePointerCast.cpp b/llvm/lib/Target/SPIRV/SPIRVLegalizePointerCast.cpp
index 5ba4fbb02560d..69051132cacff 100644
--- a/llvm/lib/Target/SPIRV/SPIRVLegalizePointerCast.cpp
+++ b/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;
diff --git a/llvm/test/CodeGen/SPIRV/pointers/getelementptr-downcast-vector.ll b/llvm/test/CodeGen/SPIRV/pointers/getelementptr-downcast-vector.ll
index d4131fa8a2658..1287a512ac96d 100644
--- a/llvm/test/CodeGen/SPIRV/pointers/getelementptr-downcast-vector.ll
+++ b/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]]