[POWERPC] Fixes an error in the handling of the MTVSRBMI instruction for big-endian #151565
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@llvm/pr-subscribers-backend-powerpc Author: zhijian lin (diggerlin) ChangesThe patch fixed a bug introduced patch [PowePC] using MTVSRBMI instruction instead of constant pool in power10+. The issue arose because the layout of vector register elements differs between little-endian and big-endian modes — specifically, the elements appear in reverse order. This led to incorrect behavior when loading constants using MTVSRBMI in big-endian configurations. Full diff: https://github.com/llvm/llvm-project/pull/151565.diff 2 Files Affected:
diff --git a/llvm/lib/Target/PowerPC/PPCISelLowering.cpp b/llvm/lib/Target/PowerPC/PPCISelLowering.cpp
index 459525ed4ee9a..0579630ee3cde 100644
--- a/llvm/lib/Target/PowerPC/PPCISelLowering.cpp
+++ b/llvm/lib/Target/PowerPC/PPCISelLowering.cpp
@@ -9586,12 +9586,14 @@ static bool isValidSplatLoad(const PPCSubtarget &Subtarget, const SDValue &Op,
return false;
}
-bool isValidMtVsrBmi(APInt &BitMask, BuildVectorSDNode &BVN) {
+bool isValidMtVsrBmi(APInt &BitMask, BuildVectorSDNode &BVN,
+ bool IsLittleEndian) {
assert(BVN.getNumOperands() > 0 && "Unexpected 0-size build vector");
BitMask.clearAllBits();
EVT VT = BVN.getValueType(0);
- APInt ConstValue(VT.getSizeInBits(), 0);
+ unsigned VTSize = VT.getSizeInBits();
+ APInt ConstValue(VTSize, 0);
unsigned EltWidth = VT.getScalarSizeInBits();
@@ -9602,7 +9604,8 @@ bool isValidMtVsrBmi(APInt &BitMask, BuildVectorSDNode &BVN) {
if (!CN)
return false;
- ConstValue.insertBits(CN->getAPIntValue().zextOrTrunc(EltWidth), BitPos);
+ ConstValue.insertBits(CN->getAPIntValue().zextOrTrunc(EltWidth),
+ IsLittleEndian ? BitPos : VTSize - EltWidth - BitPos);
BitPos += EltWidth;
}
@@ -9633,7 +9636,8 @@ SDValue PPCTargetLowering::LowerBUILD_VECTOR(SDValue Op,
// we do not convert it to MTVSRBMI.
// The xxleqv instruction sets a vector with all ones.
// The xxlxor instruction sets a vector with all zeros.
- if (isValidMtVsrBmi(BitMask, *BVN) && BitMask != 0 && BitMask != 0xffff) {
+ if (isValidMtVsrBmi(BitMask, *BVN, Subtarget.isLittleEndian()) &&
+ BitMask != 0 && BitMask != 0xffff) {
SDValue SDConstant = DAG.getTargetConstant(BitMask, dl, MVT::i32);
MachineSDNode *MSDNode =
DAG.getMachineNode(PPC::MTVSRBMI, dl, MVT::v16i8, SDConstant);
diff --git a/llvm/test/CodeGen/PowerPC/mtvsrbmi.ll b/llvm/test/CodeGen/PowerPC/mtvsrbmi.ll
index 232014db9a012..a9503f77c3090 100644
--- a/llvm/test/CodeGen/PowerPC/mtvsrbmi.ll
+++ b/llvm/test/CodeGen/PowerPC/mtvsrbmi.ll
@@ -2,22 +2,87 @@
; Verify whether the generated assembly for the following function includes the mtvsrbmi instruction.
; vector unsigned char v00FF()
; {
-; vector unsigned char x = { 0xFF, 0,0,0, 0,0,0,0, 0,0,0,0, 0,0,0,0 };
-; return x;
+; vector unsigned char x = { 0xFF, 0,0,0, 0,0,0,0, 0,0,0,0, 0,0,0,0 };
+; return x;
+; }
+; vector unsigned short short00FF()
+; {
+; vector unsigned short x = { 0xFF, 0,0,0, 0,0,0,0};
+; return x;
+; }
+; vector unsigned int int00FF()
+; {
+; vector unsigned int x = { 0xFF, 0,0,0};
+; return x;
+; }
+; vector unsigned long long longlong00FF()
+; {
+; vector unsigned long long x = { 0xFF, 0};
+; return x;
; }
; RUN: llc < %s -ppc-asm-full-reg-names -mtriple=powerpc-ibm-aix -mcpu=pwr10 -verify-machineinstrs \
-; RUN: | FileCheck %s --check-prefix=CHECK
+; RUN: | FileCheck %s --check-prefixes=CHECK,CHECK-BE
+
+; RUN: llc < %s -ppc-asm-full-reg-names -mtriple=powerpc64le-unknown-gnu-linux -mcpu=pwr10 -verify-machineinstrs \
+; RUN: | FileCheck %s --check-prefixes=CHECK,CHECK-LE
+
+; CHECK-NOT: .byte 255
+; CHECK-NOT: .byte 0
define dso_local noundef range(i8 -1, 1) <16 x i8> @_Z5v00FFv() {
-; CHECK-NOT: L..CPI0_0:
-; CHECK-NOT: .byte 255 # 0xff
-; CHECK-NOT: .byte 0 # 0x0
-
-; CHECK-LABEL: _Z5v00FFv:
-; CHECK: # %bb.0: # %entry
-; CHECK-NEXT: mtvsrbmi v2, 1
-; CHECK-NEXT: blr
+; CHECK-BE-LABEL: _Z5v00FFv:
+; CHECK-BE: # %bb.0: # %entry
+; CHECK-BE-NEXT: mtvsrbmi v2, 32768
+; CHECK-BE-NEXT: blr
+;
+; CHECK-LE-LABEL: _Z5v00FFv:
+; CHECK-LE: # %bb.0: # %entry
+; CHECK-LE-NEXT: mtvsrbmi v2, 1
+; CHECK-LE-NEXT: blr
+
entry:
ret <16 x i8> <i8 -1, i8 0, i8 0, i8 0, i8 0, i8 0, i8 0, i8 0, i8 0, i8 0, i8 0, i8 0, i8 0, i8 0, i8 0, i8 0>
}
+
+define dso_local noundef range(i16 0, 256) <8 x i16> @_Z9short00FFv() {
+; CHECK-BE-LABEL: _Z9short00FFv:
+; CHECK-BE: # %bb.0: # %entry
+; CHECK-BE-NEXT: mtvsrbmi v2, 16384
+; CHECK-BE-NEXT: blr
+;
+; CHECK-LE-LABEL: _Z9short00FFv:
+; CHECK-LE: # %bb.0: # %entry
+; CHECK-LE-NEXT: mtvsrbmi v2, 1
+; CHECK-LE-NEXT: blr
+entry:
+ ret <8 x i16> <i16 255, i16 0, i16 0, i16 0, i16 0, i16 0, i16 0, i16 0>
+}
+
+define dso_local noundef range(i32 0, 256) <4 x i32> @_Z7int00FFv() {
+; CHECK-BE-LABEL: _Z7int00FFv:
+; CHECK-BE: # %bb.0: # %entry
+; CHECK-BE-NEXT: mtvsrbmi v2, 4096
+; CHECK-BE-NEXT: blr
+;
+; CHECK-LE-LABEL: _Z7int00FFv:
+; CHECK-LE: # %bb.0: # %entry
+; CHECK-LE-NEXT: mtvsrbmi v2, 1
+; CHECK-LE-NEXT: blr
+entry:
+ ret <4 x i32> <i32 255, i32 0, i32 0, i32 0>
+}
+
+define dso_local noundef range(i64 0, 256) <2 x i64> @_Z12longlong00FFv() {
+; CHECK-BE-LABEL: _Z12longlong00FFv:
+; CHECK-BE: # %bb.0: # %entry
+; CHECK-BE-NEXT: mtvsrbmi v2, 256
+; CHECK-BE-NEXT: blr
+;
+; CHECK-LE-LABEL: _Z12longlong00FFv:
+; CHECK-LE: # %bb.0: # %entry
+; CHECK-LE-NEXT: mtvsrbmi v2, 1
+; CHECK-LE-NEXT: blr
+entry:
+ ret <2 x i64> <i64 255, i64 0>
+}
|
lei137
approved these changes
Aug 1, 2025
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| ; CHECK-NOT: .byte 255 | ||
| ; CHECK-NOT: .byte 0 |
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As 45909ec is also in the LLVM 21.x branch, we should probably cherry-pick this fix, too. |
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/cherry-pick 23b3203 |
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Error: Command failed due to missing milestone. |
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/cherry-pick 23b3203 |
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/pull-request #154138 |
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Aug 21, 2025
…for big-endian (llvm#151565) The patch fixed a bug introduced patch [[PowePC] using MTVSRBMI instruction instead of constant pool in power10+](llvm#144084 (comment)). The issue arose because the layout of vector register elements differs between little-endian and big-endian modes — specifically, the elements appear in reverse order. This led to incorrect behavior when loading constants using MTVSRBMI in big-endian configurations. (cherry picked from commit 23b3203)
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The patch fixed a bug introduced patch [PowePC] using MTVSRBMI instruction instead of constant pool in power10+.
The issue arose because the layout of vector register elements differs between little-endian and big-endian modes — specifically, the elements appear in reverse order. This led to incorrect behavior when loading constants using MTVSRBMI in big-endian configurations.