[llvm] [PowerPC] Mask constant operands in ValueBit tracking (PR #67653)
Qiu Chaofan via llvm-commits
llvm-commits at lists.llvm.org
Thu Sep 28 02:35:58 PDT 2023
https://github.com/ecnelises created https://github.com/llvm/llvm-project/pull/67653
In IR or C code, left/right shift amount larger than value size is undefined behavior. But in practise, backend lowering for srl_parts/sra_parts/shl_parts produces add/sub of shift amounts, thus constant shift amounts might be negative or larger than value size. And the lowering depends on behavior in ISA.
PowerPC ISA says, the lowest 7 bits (6 bits if in 32-bit instruction) will be taken, and if the highest among them is 1, result will be zero, otherwise the low 6 bits (or 5 on 32-bit) are used as shift amount.
This patch emulates the behavior and avoids array overflow in bit permutation's value bits calculator.
Migrated from https://reviews.llvm.org/D138551
Fixes #59074
>From 13aeaba6c21c7e3db8fcd3a4c5c2f9dfdb23f391 Mon Sep 17 00:00:00 2001
From: Qiu Chaofan <qiucofan at cn.ibm.com>
Date: Thu, 28 Sep 2023 17:33:01 +0800
Subject: [PATCH] [PowerPC] Mask constant operands in ValueBit tracking
In IR or C code, left/right shift amount larger than value size is
undefined behavior. But in practise, backend lowering for
srl_parts/sra_parts/shl_parts produces add/sub of shift amounts, thus
constant shift amounts might be negative or larger than value size. And
the lowering depends on behavior in ISA.
PowerPC ISA says, the lowest 7 bits (6 bits if in 32-bit instruction)
will be taken, and if the highest among them is 1, result will be zero,
otherwise the low 6 bits (or 5 on 32-bit) are used as shift amount.
This patch emulates the behavior and avoids array overflow in bit
permutation's value bits calculator.
---
llvm/lib/Target/PowerPC/PPCISelDAGToDAG.cpp | 36 ++++--
llvm/test/CodeGen/PowerPC/pr59074.ll | 132 ++++++++++++++++++++
2 files changed, 155 insertions(+), 13 deletions(-)
create mode 100644 llvm/test/CodeGen/PowerPC/pr59074.ll
diff --git a/llvm/lib/Target/PowerPC/PPCISelDAGToDAG.cpp b/llvm/lib/Target/PowerPC/PPCISelDAGToDAG.cpp
index b57d185bb638b8c..7f2f5affa5888bd 100644
--- a/llvm/lib/Target/PowerPC/PPCISelDAGToDAG.cpp
+++ b/llvm/lib/Target/PowerPC/PPCISelDAGToDAG.cpp
@@ -1635,7 +1635,7 @@ class BitPermutationSelector {
default: break;
case ISD::ROTL:
if (isa<ConstantSDNode>(V.getOperand(1))) {
- unsigned RotAmt = V.getConstantOperandVal(1);
+ unsigned RotAmt = V.getConstantOperandVal(1) & (NumBits - 1);
const auto &LHSBits = *getValueBits(V.getOperand(0), NumBits).second;
@@ -1648,15 +1648,20 @@ class BitPermutationSelector {
case ISD::SHL:
case PPCISD::SHL:
if (isa<ConstantSDNode>(V.getOperand(1))) {
- unsigned ShiftAmt = V.getConstantOperandVal(1);
+ // sld takes 7 bits, slw takes 6.
+ unsigned ShiftAmt = V.getConstantOperandVal(1) & ((NumBits << 1) - 1);
const auto &LHSBits = *getValueBits(V.getOperand(0), NumBits).second;
- for (unsigned i = ShiftAmt; i < NumBits; ++i)
- Bits[i] = LHSBits[i - ShiftAmt];
-
- for (unsigned i = 0; i < ShiftAmt; ++i)
- Bits[i] = ValueBit(ValueBit::ConstZero);
+ if (ShiftAmt >= NumBits) {
+ for (unsigned i = 0; i < NumBits; ++i)
+ Bits[i] = ValueBit(ValueBit::ConstZero);
+ } else {
+ for (unsigned i = ShiftAmt; i < NumBits; ++i)
+ Bits[i] = LHSBits[i - ShiftAmt];
+ for (unsigned i = 0; i < ShiftAmt; ++i)
+ Bits[i] = ValueBit(ValueBit::ConstZero);
+ }
return std::make_pair(Interesting = true, &Bits);
}
@@ -1664,15 +1669,20 @@ class BitPermutationSelector {
case ISD::SRL:
case PPCISD::SRL:
if (isa<ConstantSDNode>(V.getOperand(1))) {
- unsigned ShiftAmt = V.getConstantOperandVal(1);
+ // srd takes lowest 7 bits, srw takes 6.
+ unsigned ShiftAmt = V.getConstantOperandVal(1) & ((NumBits << 1) - 1);
const auto &LHSBits = *getValueBits(V.getOperand(0), NumBits).second;
- for (unsigned i = 0; i < NumBits - ShiftAmt; ++i)
- Bits[i] = LHSBits[i + ShiftAmt];
-
- for (unsigned i = NumBits - ShiftAmt; i < NumBits; ++i)
- Bits[i] = ValueBit(ValueBit::ConstZero);
+ if (ShiftAmt >= NumBits) {
+ for (unsigned i = 0; i < NumBits; ++i)
+ Bits[i] = ValueBit(ValueBit::ConstZero);
+ } else {
+ for (unsigned i = 0; i < NumBits - ShiftAmt; ++i)
+ Bits[i] = LHSBits[i + ShiftAmt];
+ for (unsigned i = NumBits - ShiftAmt; i < NumBits; ++i)
+ Bits[i] = ValueBit(ValueBit::ConstZero);
+ }
return std::make_pair(Interesting = true, &Bits);
}
diff --git a/llvm/test/CodeGen/PowerPC/pr59074.ll b/llvm/test/CodeGen/PowerPC/pr59074.ll
new file mode 100644
index 000000000000000..3e328c6ad9f0ba8
--- /dev/null
+++ b/llvm/test/CodeGen/PowerPC/pr59074.ll
@@ -0,0 +1,132 @@
+; NOTE: Assertions have been autogenerated by utils/update_llc_test_checks.py
+; RUN: llc -mtriple=powerpc64le-unknown-linux-gnu -mcpu=pwr7 < %s | FileCheck %s --check-prefix=LE64
+; RUN: llc -mtriple=powerpcle-unknown-linux-gnu -mcpu=pwr7 < %s | FileCheck %s --check-prefix=LE32
+; RUN: llc -mtriple=powerpc64-ibm-aix -mcpu=pwr7 < %s | FileCheck %s --check-prefix=BE64
+; RUN: llc -mtriple=powerpc-ibm-aix -mcpu=pwr7 < %s | FileCheck %s --check-prefix=BE32
+
+; To verify this doesn't crash due to array out of bound.
+define void @pr59074(ptr %0) {
+; LE64-LABEL: pr59074:
+; LE64: # %bb.0: # %entry
+; LE64-NEXT: lwz 6, 0(3)
+; LE64-NEXT: li 7, 12
+; LE64-NEXT: ld 4, 16(3)
+; LE64-NEXT: ld 5, 24(3)
+; LE64-NEXT: addi 6, 6, -12
+; LE64-NEXT: std 4, 16(3)
+; LE64-NEXT: std 5, 24(3)
+; LE64-NEXT: srd 6, 7, 6
+; LE64-NEXT: li 7, 0
+; LE64-NEXT: std 7, 8(3)
+; LE64-NEXT: std 6, 0(3)
+; LE64-NEXT: blr
+;
+; LE32-LABEL: pr59074:
+; LE32: # %bb.0: # %entry
+; LE32-NEXT: stwu 1, -80(1)
+; LE32-NEXT: .cfi_def_cfa_offset 80
+; LE32-NEXT: lwz 4, 0(3)
+; LE32-NEXT: xxlxor 0, 0, 0
+; LE32-NEXT: li 5, 4
+; LE32-NEXT: addi 6, 1, 16
+; LE32-NEXT: li 7, 0
+; LE32-NEXT: li 8, 12
+; LE32-NEXT: xxswapd 0, 0
+; LE32-NEXT: addi 4, 4, -12
+; LE32-NEXT: rlwinm 9, 4, 29, 28, 31
+; LE32-NEXT: stxvd2x 0, 6, 5
+; LE32-NEXT: stw 7, 44(1)
+; LE32-NEXT: stw 7, 40(1)
+; LE32-NEXT: stw 7, 36(1)
+; LE32-NEXT: stw 8, 16(1)
+; LE32-NEXT: lwzux 5, 9, 6
+; LE32-NEXT: li 6, 7
+; LE32-NEXT: lwz 7, 8(9)
+; LE32-NEXT: nand 6, 4, 6
+; LE32-NEXT: lwz 8, 4(9)
+; LE32-NEXT: clrlwi 4, 4, 29
+; LE32-NEXT: lwz 9, 12(9)
+; LE32-NEXT: clrlwi 6, 6, 27
+; LE32-NEXT: subfic 11, 4, 32
+; LE32-NEXT: srw 5, 5, 4
+; LE32-NEXT: slwi 10, 7, 1
+; LE32-NEXT: srw 7, 7, 4
+; LE32-NEXT: slw 6, 10, 6
+; LE32-NEXT: srw 10, 8, 4
+; LE32-NEXT: slw 8, 8, 11
+; LE32-NEXT: slw 11, 9, 11
+; LE32-NEXT: srw 4, 9, 4
+; LE32-NEXT: or 5, 8, 5
+; LE32-NEXT: or 7, 11, 7
+; LE32-NEXT: or 6, 10, 6
+; LE32-NEXT: stw 4, 12(3)
+; LE32-NEXT: stw 7, 8(3)
+; LE32-NEXT: stw 5, 0(3)
+; LE32-NEXT: stw 6, 4(3)
+; LE32-NEXT: addi 1, 1, 80
+; LE32-NEXT: blr
+;
+; BE64-LABEL: pr59074:
+; BE64: # %bb.0: # %entry
+; BE64-NEXT: lwz 6, 12(3)
+; BE64-NEXT: li 7, 12
+; BE64-NEXT: ld 4, 24(3)
+; BE64-NEXT: ld 5, 16(3)
+; BE64-NEXT: addi 6, 6, -12
+; BE64-NEXT: std 4, 24(3)
+; BE64-NEXT: std 5, 16(3)
+; BE64-NEXT: srd 6, 7, 6
+; BE64-NEXT: li 7, 0
+; BE64-NEXT: std 7, 0(3)
+; BE64-NEXT: std 6, 8(3)
+; BE64-NEXT: blr
+;
+; BE32-LABEL: pr59074:
+; BE32: # %bb.0: # %entry
+; BE32-NEXT: lwz 4, 12(3)
+; BE32-NEXT: xxlxor 0, 0, 0
+; BE32-NEXT: addi 5, 1, -64
+; BE32-NEXT: li 6, 12
+; BE32-NEXT: li 7, 0
+; BE32-NEXT: addi 8, 1, -48
+; BE32-NEXT: li 10, 7
+; BE32-NEXT: stxvw4x 0, 0, 5
+; BE32-NEXT: addi 4, 4, -12
+; BE32-NEXT: stw 6, -36(1)
+; BE32-NEXT: stw 7, -40(1)
+; BE32-NEXT: stw 7, -44(1)
+; BE32-NEXT: rlwinm 9, 4, 29, 28, 31
+; BE32-NEXT: stw 7, -48(1)
+; BE32-NEXT: sub 5, 8, 9
+; BE32-NEXT: nand 6, 4, 10
+; BE32-NEXT: clrlwi 4, 4, 29
+; BE32-NEXT: clrlwi 6, 6, 27
+; BE32-NEXT: lwz 7, 4(5)
+; BE32-NEXT: lwz 8, 8(5)
+; BE32-NEXT: lwz 9, 0(5)
+; BE32-NEXT: lwz 5, 12(5)
+; BE32-NEXT: slwi 10, 7, 1
+; BE32-NEXT: srw 11, 8, 4
+; BE32-NEXT: srw 7, 7, 4
+; BE32-NEXT: srw 5, 5, 4
+; BE32-NEXT: slw 6, 10, 6
+; BE32-NEXT: subfic 10, 4, 32
+; BE32-NEXT: srw 4, 9, 4
+; BE32-NEXT: slw 8, 8, 10
+; BE32-NEXT: slw 10, 9, 10
+; BE32-NEXT: or 6, 11, 6
+; BE32-NEXT: or 7, 10, 7
+; BE32-NEXT: or 5, 8, 5
+; BE32-NEXT: stw 4, 0(3)
+; BE32-NEXT: stw 6, 8(3)
+; BE32-NEXT: stw 5, 12(3)
+; BE32-NEXT: stw 7, 4(3)
+; BE32-NEXT: blr
+entry:
+ %v1 = load <2 x i128>, <2 x i128>* %0
+ %v2 = insertelement <2 x i128> %v1, i128 12, i32 0
+ %v3 = sub <2 x i128> %v1, %v2
+ %v4 = lshr <2 x i128> %v2, %v3
+ store <2 x i128> %v4, <2 x i128>* %0
+ ret void
+}
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