[llvm] 44b260c - [X86] Increase the number of instructions searched for isSafeToClobberEFLAGS in a couple places

[Craig Topper via llvm-commits]

Author: Craig Topper
Date: 2020-08-08T11:29:41-07:00
New Revision: 44b260cb0aab387d85e4d59c16fc7b8866264f5e

URL: https://github.com/llvm/llvm-project/commit/44b260cb0aab387d85e4d59c16fc7b8866264f5e
DIFF: https://github.com/llvm/llvm-project/commit/44b260cb0aab387d85e4d59c16fc7b8866264f5e.diff

LOG: [X86] Increase the number of instructions searched for isSafeToClobberEFLAGS in a couple places

Previously this function searched 4 instructions forwards or
backwards to determine if it was ok to clobber eflags.

This is called in 3 places: rematerialization, turning 2 operand
leas into adds or splitting 3 ops leas into an lea and add on some
CPU targets.

This patch increases the search limit to 10 instructions for
rematerialization and 2 operand lea to add. I've left the old
treshold for 3 ops lea spliting as that increases code size.

Fixes PR47024 and PR43014

Added: 
    

Modified: 
    llvm/lib/Target/X86/X86FixupLEAs.cpp
    llvm/lib/Target/X86/X86InstrInfo.cpp
    llvm/lib/Target/X86/X86InstrInfo.h
    llvm/test/CodeGen/X86/optimize-max-0.ll

Removed: 
    


################################################################################
diff  --git a/llvm/lib/Target/X86/X86FixupLEAs.cpp b/llvm/lib/Target/X86/X86FixupLEAs.cpp
index 424279038921..fcc3e8f781a3 100644
--- a/llvm/lib/Target/X86/X86FixupLEAs.cpp
+++ b/llvm/lib/Target/X86/X86FixupLEAs.cpp
@@ -376,7 +376,7 @@ bool FixupLEAPass::optTwoAddrLEA(MachineBasicBlock::iterator &I,
   const MachineOperand &Segment = MI.getOperand(1 + X86::AddrSegmentReg);
 
   if (Segment.getReg() != 0 || !Disp.isImm() || Scale.getImm() > 1 ||
-      !TII->isSafeToClobberEFLAGS(MBB, I))
+      !TII->isSafeToClobberEFLAGS(MBB, I, 10))
     return false;
 
   Register DestReg = MI.getOperand(0).getReg();

diff  --git a/llvm/lib/Target/X86/X86InstrInfo.cpp b/llvm/lib/Target/X86/X86InstrInfo.cpp
index c753880fc92c..b27959ad9bf5 100644
--- a/llvm/lib/Target/X86/X86InstrInfo.cpp
+++ b/llvm/lib/Target/X86/X86InstrInfo.cpp
@@ -1127,7 +1127,7 @@ void X86InstrInfo::reMaterialize(MachineBasicBlock &MBB,
                                  const MachineInstr &Orig,
                                  const TargetRegisterInfo &TRI) const {
   bool ClobbersEFLAGS = Orig.modifiesRegister(X86::EFLAGS, &TRI);
-  if (ClobbersEFLAGS && !isSafeToClobberEFLAGS(MBB, I)) {
+  if (ClobbersEFLAGS && !isSafeToClobberEFLAGS(MBB, I, 10)) {
     // The instruction clobbers EFLAGS. Re-materialize as MOV32ri to avoid side
     // effects.
     int Value;

diff  --git a/llvm/lib/Target/X86/X86InstrInfo.h b/llvm/lib/Target/X86/X86InstrInfo.h
index c345a8217168..60b7d51bf9e4 100644
--- a/llvm/lib/Target/X86/X86InstrInfo.h
+++ b/llvm/lib/Target/X86/X86InstrInfo.h
@@ -442,8 +442,9 @@ class X86InstrInfo final : public X86GenInstrInfo {
   /// conservative. If it cannot definitely determine the safety after visiting
   /// a few instructions in each direction it assumes it's not safe.
   bool isSafeToClobberEFLAGS(MachineBasicBlock &MBB,
-                             MachineBasicBlock::iterator I) const {
-    return MBB.computeRegisterLiveness(&RI, X86::EFLAGS, I, 4) ==
+                             MachineBasicBlock::iterator I,
+                             unsigned Neighborhood = 4) const {
+    return MBB.computeRegisterLiveness(&RI, X86::EFLAGS, I, Neighborhood) ==
            MachineBasicBlock::LQR_Dead;
   }
 

diff  --git a/llvm/test/CodeGen/X86/optimize-max-0.ll b/llvm/test/CodeGen/X86/optimize-max-0.ll
index e7f885625b76..5367f390d1cb 100644
--- a/llvm/test/CodeGen/X86/optimize-max-0.ll
+++ b/llvm/test/CodeGen/X86/optimize-max-0.ll
@@ -85,7 +85,7 @@ define void @foo(i8* %r, i32 %s, i32 %w, i32 %x, i8* %j, i32 %d) nounwind {
 ; CHECK-NEXT:    movl {{[-0-9]+}}(%e{{[sb]}}p), %eax ## 4-byte Reload
 ; CHECK-NEXT:    addl %ecx, %eax
 ; CHECK-NEXT:    movl {{[0-9]+}}(%esp), %esi
-; CHECK-NEXT:    leal 2(%esi), %esi
+; CHECK-NEXT:    addl $2, %esi
 ; CHECK-NEXT:    movl %esi, {{[-0-9]+}}(%e{{[sb]}}p) ## 4-byte Spill
 ; CHECK-NEXT:    movl (%esp), %esi ## 4-byte Reload
 ; CHECK-NEXT:    addl %esi, %ecx
@@ -513,7 +513,7 @@ define void @bar(i8* %r, i32 %s, i32 %w, i32 %x, i8* %j, i32 %d) nounwind {
 ; CHECK-NEXT:    movl {{[-0-9]+}}(%e{{[sb]}}p), %ecx ## 4-byte Reload
 ; CHECK-NEXT:    addl %eax, %ecx
 ; CHECK-NEXT:    movl {{[0-9]+}}(%esp), %edx
-; CHECK-NEXT:    leal 2(%edx), %edx
+; CHECK-NEXT:    addl $2, %edx
 ; CHECK-NEXT:    movl %edx, {{[-0-9]+}}(%e{{[sb]}}p) ## 4-byte Spill
 ; CHECK-NEXT:    movl {{[-0-9]+}}(%e{{[sb]}}p), %edx ## 4-byte Reload
 ; CHECK-NEXT:    addl %edx, %eax