[llvm-commits] [llvm] r128179 - in /llvm/trunk: lib/Target/ARM/ARMBaseInstrInfo.cpp test/CodeGen/ARM/2011-03-23-PeepholeBug.ll test/CodeGen/ARM/long_shift.ll
Evan Cheng
evan.cheng at apple.com
Wed Mar 23 15:52:04 PDT 2011
Author: evancheng
Date: Wed Mar 23 17:52:04 2011
New Revision: 128179
URL: http://llvm.org/viewvc/llvm-project?rev=128179&view=rev
Log:
Cmp peephole optimization isn't always safe for signed arithmetics.
int tries = INT_MAX;
while (tries > 0) {
tries--;
}
The check should be:
subs r4, #1
cmp r4, #0
bgt LBB0_1
The subs can set the overflow V bit when r4 is INT_MAX+1 (which loop
canonicalization apparently does in this case). cmp #0 would have cleared
it while not changing the N and Z bits. Since BGT is dependent on the V
bit, i.e. (N == V) && !Z, it is not safe to eliminate the cmp #0.
rdar://9172742
Added:
llvm/trunk/test/CodeGen/ARM/2011-03-23-PeepholeBug.ll
Modified:
llvm/trunk/lib/Target/ARM/ARMBaseInstrInfo.cpp
llvm/trunk/test/CodeGen/ARM/long_shift.ll
Modified: llvm/trunk/lib/Target/ARM/ARMBaseInstrInfo.cpp
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Target/ARM/ARMBaseInstrInfo.cpp?rev=128179&r1=128178&r2=128179&view=diff
==============================================================================
--- llvm/trunk/lib/Target/ARM/ARMBaseInstrInfo.cpp (original)
+++ llvm/trunk/lib/Target/ARM/ARMBaseInstrInfo.cpp Wed Mar 23 17:52:04 2011
@@ -1612,11 +1612,51 @@
switch (MI->getOpcode()) {
default: break;
case ARM::ADDri:
- case ARM::ANDri:
- case ARM::t2ANDri:
case ARM::SUBri:
case ARM::t2ADDri:
- case ARM::t2SUBri:
+ case ARM::t2SUBri: {
+ // Scan forward for the use of CPSR, if it's a conditional code requires
+ // checking of V bit, then this is not safe to do. If we can't find the
+ // CPSR use (i.e. used in another block), then it's not safe to perform
+ // the optimization.
+ bool isSafe = false;
+ I = CmpInstr;
+ E = MI->getParent()->end();
+ while (!isSafe && ++I != E) {
+ const MachineInstr &Instr = *I;
+ for (unsigned IO = 0, EO = Instr.getNumOperands();
+ !isSafe && IO != EO; ++IO) {
+ const MachineOperand &MO = Instr.getOperand(IO);
+ if (!MO.isReg() || MO.getReg() != ARM::CPSR)
+ continue;
+ if (MO.isDef()) {
+ isSafe = true;
+ break;
+ }
+ // Condition code is after the operand before CPSR.
+ ARMCC::CondCodes CC = (ARMCC::CondCodes)Instr.getOperand(IO-1).getImm();
+ switch (CC) {
+ default:
+ isSafe = true;
+ break;
+ case ARMCC::VS:
+ case ARMCC::VC:
+ case ARMCC::GE:
+ case ARMCC::LT:
+ case ARMCC::GT:
+ case ARMCC::LE:
+ return false;
+ }
+ }
+ }
+
+ if (!isSafe)
+ return false;
+
+ // fallthrough
+ }
+ case ARM::ANDri:
+ case ARM::t2ANDri:
// Toggle the optional operand to CPSR.
MI->getOperand(5).setReg(ARM::CPSR);
MI->getOperand(5).setIsDef(true);
Added: llvm/trunk/test/CodeGen/ARM/2011-03-23-PeepholeBug.ll
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/test/CodeGen/ARM/2011-03-23-PeepholeBug.ll?rev=128179&view=auto
==============================================================================
--- llvm/trunk/test/CodeGen/ARM/2011-03-23-PeepholeBug.ll (added)
+++ llvm/trunk/test/CodeGen/ARM/2011-03-23-PeepholeBug.ll Wed Mar 23 17:52:04 2011
@@ -0,0 +1,41 @@
+; RUN: llc < %s -mtriple=thumbv7-apple-darwin10 -relocation-model=pic -disable-fp-elim -mcpu=cortex-a8 | FileCheck %s
+
+; subs r4, #1
+; cmp r4, 0
+; bgt
+; cmp cannot be optimized away since it will clear the overflow bit.
+; gt / ge, lt, le conditions all depend on V bit.
+; rdar://9172742
+
+define i32 @t() nounwind {
+; CHECK: t:
+entry:
+ br label %bb2
+
+bb: ; preds = %bb2
+ %0 = tail call i32 @rand() nounwind
+ %1 = icmp eq i32 %0, 50
+ br i1 %1, label %bb3, label %bb1
+
+bb1: ; preds = %bb
+ %tmp = tail call i32 @puts() nounwind
+ %indvar.next = add i32 %indvar, 1
+ br label %bb2
+
+bb2: ; preds = %bb1, %entry
+; CHECK: bb2
+; CHECK: subs [[REG:r[0-9]+]], #1
+; CHECK: cmp [[REG]], #0
+; CHECK: bgt
+ %indvar = phi i32 [ %indvar.next, %bb1 ], [ 0, %entry ]
+ %tries.0 = sub i32 2147483647, %indvar
+ %tmp1 = icmp sgt i32 %tries.0, 0
+ br i1 %tmp1, label %bb, label %bb3
+
+bb3: ; preds = %bb2, %bb
+ ret i32 0
+}
+
+declare i32 @rand()
+
+declare i32 @puts() nounwind
Modified: llvm/trunk/test/CodeGen/ARM/long_shift.ll
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/test/CodeGen/ARM/long_shift.ll?rev=128179&r1=128178&r2=128179&view=diff
==============================================================================
--- llvm/trunk/test/CodeGen/ARM/long_shift.ll (original)
+++ llvm/trunk/test/CodeGen/ARM/long_shift.ll Wed Mar 23 17:52:04 2011
@@ -24,7 +24,8 @@
; CHECK: f2
; CHECK: lsr{{.*}}r2
; CHECK-NEXT: rsb r3, r2, #32
-; CHECK-NEXT: subs r2, r2, #32
+; CHECK-NEXT: sub r2, r2, #32
+; CHECK-NEXT: cmp r2, #0
; CHECK-NEXT: orr r0, r0, r1, lsl r3
; CHECK-NEXT: asrge r0, r1, r2
%a = ashr i64 %x, %y
@@ -36,7 +37,8 @@
; CHECK: f3
; CHECK: lsr{{.*}}r2
; CHECK-NEXT: rsb r3, r2, #32
-; CHECK-NEXT: subs r2, r2, #32
+; CHECK-NEXT: sub r2, r2, #32
+; CHECK-NEXT: cmp r2, #0
; CHECK-NEXT: orr r0, r0, r1, lsl r3
; CHECK-NEXT: lsrge r0, r1, r2
%a = lshr i64 %x, %y
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