[X86] Make sure SF is updated when optimizing for `jg/jge/jl/jle`

This fixes issue #56103.

Reviewed By: mingmingl

Differential Revision: https://reviews.llvm.org/D128122

2 files changed, 70 insertions, 0 deletions

diff --git a/llvm/lib/Target/X86/X86InstrInfo.cpp b/llvm/lib/Target/X86/X86InstrInfo.cpp
index f2101ea..ec32ac2 100644
--- a/llvm/lib/Target/X86/X86InstrInfo.cpp
+++ b/llvm/lib/Target/X86/X86InstrInfo.cpp
@@ -4462,6 +4462,11 @@ bool X86InstrInfo::optimizeCompareInstr(MachineInstr &CmpInstr, Register SrcReg,
         return false;
       case X86::COND_G: case X86::COND_GE:
       case X86::COND_L: case X86::COND_LE:
+        // If SF is used, but the instruction doesn't update the SF, then we
+        // can't do the optimization.
+        if (NoSignFlag)
+          return false;
+        LLVM_FALLTHROUGH;
       case X86::COND_O: case X86::COND_NO:
         // If OF is used, the instruction needs to clear it like CmpZero does.
         if (!ClearsOverflowFlag)
diff --git a/llvm/test/CodeGen/X86/pr56103.ll b/llvm/test/CodeGen/X86/pr56103.ll
new file mode 100644
index 0000000..3d979a0
--- /dev/null
+++ b/llvm/test/CodeGen/X86/pr56103.ll
@@ -0,0 +1,65 @@
+; NOTE: Assertions have been autogenerated by utils/update_llc_test_checks.py
+; RUN: llc < %s -mtriple=x86_64-linux-generic | FileCheck %s
+
+@e = global i16 0, align 2
+@a = global i32 0, align 4
+@c = global i32 0, align 4
+@b = global i64 0, align 8
+
+; Check the test instruction won't be optimizated by peephole opt.
+
+define dso_local i32 @main() nounwind {
+; CHECK-LABEL: main:
+; CHECK:       # %bb.0: # %entry
+; CHECK-NEXT:    pushq %rax
+; CHECK-NEXT:    movq e@GOTPCREL(%rip), %rax
+; CHECK-NEXT:    movw $1, (%rax)
+; CHECK-NEXT:    movq b@GOTPCREL(%rip), %rax
+; CHECK-NEXT:    movq $1, (%rax)
+; CHECK-NEXT:    movq a@GOTPCREL(%rip), %rax
+; CHECK-NEXT:    movl (%rax), %ecx
+; CHECK-NEXT:    movl $-2, %eax
+; CHECK-NEXT:    sarl %cl, %eax
+; CHECK-NEXT:    movq c@GOTPCREL(%rip), %rdx
+; CHECK-NEXT:    movl (%rdx), %edx
+; CHECK-NEXT:    decl %edx
+; CHECK-NEXT:    movzwl %ax, %eax
+; CHECK-NEXT:    decl %eax
+; CHECK-NEXT:    xorl %edx, %eax
+; CHECK-NEXT:    notl %ecx
+; CHECK-NEXT:    andl %eax, %ecx
+; CHECK-NEXT:    testq %rcx, %rcx
+; CHECK-NEXT:    jle .LBB0_2
+; CHECK-NEXT:  # %bb.1: # %if.end
+; CHECK-NEXT:    xorl %eax, %eax
+; CHECK-NEXT:    popq %rcx
+; CHECK-NEXT:    retq
+; CHECK-NEXT:  .LBB0_2: # %if.then
+; CHECK-NEXT:    callq abort@PLT
+entry:
+  store i16 1, ptr @e, align 2
+  store i64 1, ptr @b, align 8
+  %0 = load i32, ptr @a, align 4
+  %shr = ashr i32 -2, %0
+  %1 = load i32, ptr @c, align 4
+  %sub = add i32 %1, -1
+  %conv2 = zext i32 %sub to i64
+  %2 = and i32 %shr, 65535
+  %conv3 = zext i32 %2 to i64
+  %sub4 = add nsw i64 %conv3, -1
+  %xor = xor i64 %sub4, %conv2
+  %neg5 = xor i32 %0, -1
+  %conv6 = sext i32 %neg5 to i64
+  %and = and i64 %xor, %conv6
+  %cmp = icmp slt i64 %and, 1
+  br i1 %cmp, label %if.then, label %if.end
+
+if.then:                                          ; preds = %entry
+  call void @abort() #2
+  unreachable
+
+if.end:                                           ; preds = %entry
+  ret i32 0
+}
+
+declare void @abort()