[AArch64][GlobalISel] Fix miscompile of <16 x s8> G_EXTRACT_VECTOR_ELT.

When support for copying vector s8 lanes was added recently, this also
had the side effect of fixing a fallback for <16 x s8> extracts since
both used the same helper. However, there was a bug in another helper
to get the regclass for a specific FPR-native type, which was assigning
FPR16 to s8 instead of FPR8.

diff --git a/llvm/lib/Target/AArch64/GISel/AArch64InstructionSelector.cpp b/llvm/lib/Target/AArch64/GISel/AArch64InstructionSelector.cpp
index 336cb7e..bce7f94 100644 (file)
--- a/llvm/lib/Target/AArch64/GISel/AArch64InstructionSelector.cpp
+++ b/llvm/lib/Target/AArch64/GISel/AArch64InstructionSelector.cpp
@@ -496,14 +496,18 @@ getRegClassForTypeOnBank(LLT Ty, const RegisterBank &RB,
   }
 
   if (RB.getID() == AArch64::FPRRegBankID) {
-    if (Ty.getSizeInBits() <= 16)
+    switch (Ty.getSizeInBits()) {
+    case 8:
+      return &AArch64::FPR8RegClass;
+    case 16:
       return &AArch64::FPR16RegClass;
-    if (Ty.getSizeInBits() == 32)
+    case 32:
       return &AArch64::FPR32RegClass;
-    if (Ty.getSizeInBits() == 64)
+    case 64:
       return &AArch64::FPR64RegClass;
-    if (Ty.getSizeInBits() == 128)
+    case 128:
       return &AArch64::FPR128RegClass;
+    }
     return nullptr;
   }
 

diff --git a/llvm/test/CodeGen/AArch64/GlobalISel/select-extract-vector-elt.mir b/llvm/test/CodeGen/AArch64/GlobalISel/select-extract-vector-elt.mir
index 919fec7..e157c73 100644 (file)
--- a/llvm/test/CodeGen/AArch64/GlobalISel/select-extract-vector-elt.mir
+++ b/llvm/test/CodeGen/AArch64/GlobalISel/select-extract-vector-elt.mir
@@ -211,6 +211,35 @@ body:             |
     RET_ReallyLR implicit $h0
 ...
 ---
+name:            v16s8
+alignment:       4
+legalized:       true
+regBankSelected: true
+tracksRegLiveness: true
+liveins:
+  - { reg: '$q0' }
+body:             |
+  bb.1:
+    liveins: $q0
+
+    ; CHECK-LABEL: name: v16s8
+    ; CHECK: liveins: $q0
+    ; CHECK: [[COPY:%[0-9]+]]:fpr128 = COPY $q0
+    ; CHECK: [[COPY1:%[0-9]+]]:fpr8 = COPY [[COPY]].bsub
+    ; CHECK: [[SUBREG_TO_REG:%[0-9]+]]:fpr32 = SUBREG_TO_REG 0, [[COPY1]], %subreg.bsub
+    ; CHECK: [[COPY2:%[0-9]+]]:gpr32all = COPY [[SUBREG_TO_REG]]
+    ; CHECK: $w0 = COPY [[COPY2]]
+    ; CHECK: RET_ReallyLR implicit $w0
+    %0:fpr(<16 x s8>) = COPY $q0
+    %2:gpr(s64) = G_CONSTANT i64 0
+    %1:fpr(s8) = G_EXTRACT_VECTOR_ELT %0(<16 x s8>), %2(s64)
+    %4:gpr(s8) = COPY %1(s8)
+    %3:gpr(s32) = G_ANYEXT %4(s8)
+    $w0 = COPY %3(s32)
+    RET_ReallyLR implicit $w0
+
+...
+---
 name:            v2p0
 alignment:       4
 legalized:       true