[llvm-commits] [llvm] r160912 - in /llvm/trunk: lib/Target/X86/X86InstrInfo.cpp test/CodeGen/X86/jump_sign.ll

[Manman Ren]

Author: mren
Date: Fri Jul 27 22:15:46 2012
New Revision: 160912

URL: http://llvm.org/viewvc/llvm-project?rev=160912&view=rev
Log:
X86 Peephole: fix PR13475 in optimizeCompare.

It is possible that an instruction can use and update EFLAGS.
When checking the safety, we should check the usage of EFLAGS first before
declaring it is safe to optimize due to the update.


Modified:
    llvm/trunk/lib/Target/X86/X86InstrInfo.cpp
    llvm/trunk/test/CodeGen/X86/jump_sign.ll

Modified: llvm/trunk/lib/Target/X86/X86InstrInfo.cpp
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Target/X86/X86InstrInfo.cpp?rev=160912&r1=160911&r2=160912&view=diff
==============================================================================
--- llvm/trunk/lib/Target/X86/X86InstrInfo.cpp (original)
+++ llvm/trunk/lib/Target/X86/X86InstrInfo.cpp Fri Jul 27 22:15:46 2012
@@ -3221,12 +3221,15 @@
   MachineBasicBlock::iterator E = CmpInstr->getParent()->end();
   for (++I; I != E; ++I) {
     const MachineInstr &Instr = *I;
-    if (Instr.modifiesRegister(X86::EFLAGS, TRI)) {
+    bool ModifyEFLAGS = Instr.modifiesRegister(X86::EFLAGS, TRI);
+    bool UseEFLAGS = Instr.readsRegister(X86::EFLAGS, TRI);
+    // We should check the usage if this instruction uses and updates EFLAGS.
+    if (!UseEFLAGS && ModifyEFLAGS) {
       // It is safe to remove CmpInstr if EFLAGS is updated again.
       IsSafe = true;
       break;
     }
-    if (!Instr.readsRegister(X86::EFLAGS, TRI))
+    if (!UseEFLAGS && !ModifyEFLAGS)
       continue;
 
     // EFLAGS is used by this instruction.
@@ -3281,7 +3284,8 @@
       // instructions will be modified.
       OpsToUpdate.push_back(std::make_pair(&*I, NewOpc));
     }
-    if (Instr.killsRegister(X86::EFLAGS, TRI)) {
+    if (ModifyEFLAGS || Instr.killsRegister(X86::EFLAGS, TRI)) {
+      // It is safe to remove CmpInstr if EFLAGS is updated again or killed.
       IsSafe = true;
       break;
     }

Modified: llvm/trunk/test/CodeGen/X86/jump_sign.ll
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/test/CodeGen/X86/jump_sign.ll?rev=160912&r1=160911&r2=160912&view=diff
==============================================================================
--- llvm/trunk/test/CodeGen/X86/jump_sign.ll (original)
+++ llvm/trunk/test/CodeGen/X86/jump_sign.ll Fri Jul 27 22:15:46 2012
@@ -214,3 +214,19 @@
   %add. = select i1 %cmp, i32 %add, i32 0
   ret i32 %add.
 }
+; PR13475
+; If we have sub a, b and cmp b, a and the result of cmp is used
+; by sbb, we should not optimize cmp away.
+define i32 @q(i32 %j.4, i32 %w, i32 %el) {
+; CHECK: q:
+; CHECK: sub
+; CHECK: cmp
+; CHECK-NEXT: sbb
+  %tmp532 = add i32 %j.4, %w
+  %tmp533 = icmp ugt i32 %tmp532, %el
+  %tmp534 = icmp ult i32 %w, %el
+  %or.cond = and i1 %tmp533, %tmp534
+  %tmp535 = sub i32 %el, %w
+  %j.5 = select i1 %or.cond, i32 %tmp535, i32 %j.4
+  ret i32 %j.5
+}