[llvm] r236050 - ARM: fix peephole optimisation of TST
Tim Northover
tnorthover at apple.com
Tue Apr 28 15:03:55 PDT 2015
Author: tnorthover
Date: Tue Apr 28 17:03:55 2015
New Revision: 236050
URL: http://llvm.org/viewvc/llvm-project?rev=236050&view=rev
Log:
ARM: fix peephole optimisation of TST
We were trying to look through COPY instructions, but only to the next
instruction in a BB and incorrectly anyway. The cases where that would actually
be a good idea are rare enough (and not even tested!) that it's not worth
trying to get right.
rdar://20721342
Modified:
llvm/trunk/lib/Target/ARM/ARMBaseInstrInfo.cpp
llvm/trunk/test/CodeGen/ARM/arm-and-tst-peephole.ll
Modified: llvm/trunk/lib/Target/ARM/ARMBaseInstrInfo.cpp
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Target/ARM/ARMBaseInstrInfo.cpp?rev=236050&r1=236049&r2=236050&view=diff
==============================================================================
--- llvm/trunk/lib/Target/ARM/ARMBaseInstrInfo.cpp (original)
+++ llvm/trunk/lib/Target/ARM/ARMBaseInstrInfo.cpp Tue Apr 28 17:03:55 2015
@@ -2315,16 +2315,6 @@ static bool isSuitableForMask(MachineIns
if (SrcReg == MI->getOperand(CommonUse ? 1 : 0).getReg())
return true;
break;
- case ARM::COPY: {
- // Walk down one instruction which is potentially an 'and'.
- const MachineInstr &Copy = *MI;
- MachineBasicBlock::iterator AND(
- std::next(MachineBasicBlock::iterator(MI)));
- if (AND == MI->getParent()->end()) return false;
- MI = AND;
- return isSuitableForMask(MI, Copy.getOperand(0).getReg(),
- CmpMask, true);
- }
}
return false;
Modified: llvm/trunk/test/CodeGen/ARM/arm-and-tst-peephole.ll
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/test/CodeGen/ARM/arm-and-tst-peephole.ll?rev=236050&r1=236049&r2=236050&view=diff
==============================================================================
--- llvm/trunk/test/CodeGen/ARM/arm-and-tst-peephole.ll (original)
+++ llvm/trunk/test/CodeGen/ARM/arm-and-tst-peephole.ll Tue Apr 28 17:03:55 2015
@@ -8,9 +8,9 @@
%struct.Foo = type { i8* }
-; ARM: foo
-; THUMB: foo
-; T2: foo
+; ARM-LABEL: foo:
+; THUMB-LABEL: foo:
+; T2-LABEL: foo:
define %struct.Foo* @foo(%struct.Foo* %this, i32 %acc) nounwind readonly align 2 {
entry:
%scevgep = getelementptr %struct.Foo, %struct.Foo* %this, i32 1
@@ -83,9 +83,9 @@ sw.epilog:
%struct.S = type { i8* (i8*)*, [1 x i8] }
-; ARM: bar
-; THUMB: bar
-; T2: bar
+; ARM-LABEL: bar:
+; THUMB-LABEL: bar:
+; T2-LABEL: bar:
; V8-LABEL: bar:
define internal zeroext i8 @bar(%struct.S* %x, %struct.S* nocapture %y) nounwind readonly {
entry:
@@ -135,4 +135,26 @@ return:
ret i8 1
}
+
+; We were looking through multiple COPY instructions to find an AND we might
+; fold into a TST, but in doing so we changed the register being tested allowing
+; folding of unrelated tests (in this case, a TST against r1 was eliminated in
+; favour of an AND of r0).
+
+; ARM-LABEL: test_tst_assessment:
+; THUMB-LABEL: test_tst_assessment:
+; T2-LABEL: test_tst_assessment:
+; V8-LABEL: test_tst_assessment:
+define i32 @test_tst_assessment(i1 %lhs, i1 %rhs) {
+ %lhs32 = zext i1 %lhs to i32
+ %rhs32 = zext i1 %rhs to i32
+ %diff = sub nsw i32 %lhs32, %rhs32
+; ARM: tst r1, #1
+; THUMB: movs [[RTMP:r[0-9]+]], #1
+; THUMB: tst r1, [[RTMP]]
+; T2: tst.w r1, #1
+; V8: tst.w r1, #1
+ ret i32 %diff
+}
+
!1 = !{!"branch_weights", i32 1, i32 1, i32 3, i32 2 }
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