[llvm] r350223 - [PowerPC] Remove SeenUse check when optimizing conditional branch in

[Wei Mi via llvm-commits]

Author: wmi
Date: Wed Jan  2 09:07:23 2019
New Revision: 350223

URL: http://llvm.org/viewvc/llvm-project?rev=350223&view=rev
Log:
[PowerPC] Remove SeenUse check when optimizing conditional branch in
PPCPreEmitPeephole pass.

PPCPreEmitPeephole will convert a BC to B when the conditional branch is
based on a constant CR by CRSET or CRUNSET. This is added in
https://reviews.llvm.org/rL343100.

When the conditional branch is known to be always taken, all branches will
be removed and a new unconditional branch will be inserted. However, when
SeenUse is false the original patch will not remove the branches, but still
insert the new unconditional branch, update the successors and create
inconsistent IR. Compiling the synthetic testcase included can show the
problem we run into.

The patch simply removes the SeenUse condition when adding branches into
InstrsToErase set.

Differential Revision: https://reviews.llvm.org/D56041

Added:
    llvm/trunk/test/CodeGen/PowerPC/setcr_bc3.mir
Modified:
    llvm/trunk/lib/Target/PowerPC/PPCPreEmitPeephole.cpp

Modified: llvm/trunk/lib/Target/PowerPC/PPCPreEmitPeephole.cpp
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Target/PowerPC/PPCPreEmitPeephole.cpp?rev=350223&r1=350222&r2=350223&view=diff
==============================================================================
--- llvm/trunk/lib/Target/PowerPC/PPCPreEmitPeephole.cpp (original)
+++ llvm/trunk/lib/Target/PowerPC/PPCPreEmitPeephole.cpp Wed Jan  2 09:07:23 2019
@@ -140,7 +140,7 @@ namespace {
           // This conditional branch is always taken. So, remove all branches
           // and insert an unconditional branch to the destination of this.
           MachineBasicBlock::iterator It = Br, Er = MBB.end();
-          for (; It != Er && !SeenUse; It++) {
+          for (; It != Er; It++) {
             if (It->isDebugInstr()) continue;
             assert(It->isTerminator() && "Non-terminator after a terminator");
             InstrsToErase.push_back(&*It);

Added: llvm/trunk/test/CodeGen/PowerPC/setcr_bc3.mir
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/test/CodeGen/PowerPC/setcr_bc3.mir?rev=350223&view=auto
==============================================================================
--- llvm/trunk/test/CodeGen/PowerPC/setcr_bc3.mir (added)
+++ llvm/trunk/test/CodeGen/PowerPC/setcr_bc3.mir Wed Jan  2 09:07:23 2019
@@ -0,0 +1,108 @@
+# RUN: llc -verify-machineinstrs -start-before=ppc-pre-emit-peephole %s -o - | FileCheck %s
+--- |
+  target datalayout = "e-m:e-i64:64-n32:64"
+  target triple = "powerpc64le-unknown-linux-gnu"
+
+  declare signext i32 @callee(i32 signext)
+
+  define signext i32 @func(i32 signext %v) {
+    ret i32 0
+  }
+...
+---
+name:            func
+alignment:       4
+exposesReturnsTwice: false
+legalized:       false
+regBankSelected: false
+selected:        false
+failedISel:      false
+tracksRegLiveness: true
+registers:
+liveins:
+  - { reg: '$x3', virtual-reg: '' }
+frameInfo:
+  isFrameAddressTaken: false
+  isReturnAddressTaken: false
+  hasStackMap:     false
+  hasPatchPoint:   false
+  stackSize:       48
+  offsetAdjustment: 0
+  maxAlignment:    0
+  adjustsStack:    true
+  hasCalls:        true
+  stackProtector:  ''
+  maxCallFrameSize: 32
+  hasOpaqueSPAdjustment: false
+  hasVAStart:      false
+  hasMustTailInVarArgFunc: false
+  localFrameSize:  0
+  savePoint:       ''
+  restorePoint:    ''
+fixedStack:
+  - { id: 0, type: spill-slot, offset: -16, size: 8, alignment: 16, stack-id: 0, 
+      callee-saved-register: '$x30', callee-saved-restored: true, debug-info-variable: '', 
+      debug-info-expression: '', debug-info-location: '' }
+stack:
+constants:
+
+body:             |
+  bb.0:
+    successors: %bb.2(0x30000000), %bb.1(0x50000000)
+    liveins: $x3, $x30
+
+    ; bc should be converted into b
+    ; CHECK-LABEL: func
+    ; CHECK: # %bb.1
+    ; CHECK: creqv
+    ; CHECK-NOT: bc
+    ; CHECK: b .LBB0_3
+    ; CHECK: .LBB0_2
+
+    $x0 = MFLR8 implicit $lr8
+    STD killed $x0, 16, $x1
+    $x1 = STDU $x1, -48, $x1
+    STD killed $x30, 32, $x1 :: (store 8 into %fixed-stack.0, align 16)
+    $x30 = OR8 $x3, $x3
+    BL8_NOP @callee, csr_svr464_altivec, implicit-def dead $lr8, implicit $rm, implicit killed $x3, implicit $x2, implicit-def $r1, implicit-def $x3
+    renamable $cr0 = CMPLWI renamable $r3, 0
+    BCC 76, killed renamable $cr0, %bb.2
+
+  bb.1:
+    successors: %bb.5(0x40000000), %bb.2(0x40000000)
+    liveins: $x3
+
+    renamable $x3 = EXTSW_32_64 killed renamable $r3, implicit $x3
+    BL8_NOP @callee, csr_svr464_altivec, implicit-def dead $lr8, implicit $rm, implicit killed $x3, implicit $x2, implicit-def $r1, implicit-def $x3
+    renamable $cr2un = CRSET
+    $cr2gt = CROR $cr2un, $cr2un
+    $x30 = OR8 killed $x3, $x3
+    BC killed renamable $cr2un, %bb.5
+    B %bb.2
+
+  bb.4:
+    successors: %bb.5(0x80000000)
+    liveins: $x30
+
+    $x3 = LI8 0
+    BL8_NOP @callee, csr_svr464_altivec, implicit-def dead $lr8, implicit $rm, implicit killed $x3, implicit $x2, implicit-def $r1, implicit-def dead $x3
+
+  bb.5:
+    liveins: $x30, $cr0gt
+
+    renamable $x3 = EXTSW_32_64 killed renamable $r30, implicit $x30
+    $x30 = LD 32, $x1 :: (load 8 from %fixed-stack.0, align 16)
+    $x1 = ADDI8 $x1, 48
+    $x0 = LD 16, $x1
+    MTLR8 killed $x0, implicit-def $lr8
+    BLR8 implicit $lr8, implicit $rm, implicit killed $x3
+
+  bb.2:
+    successors: %bb.5(0x40000000), %bb.4(0x40000000)
+    liveins: $x30
+
+    renamable $cr0 = CMPWI renamable $r30, -1
+    BCn killed renamable $cr0gt, %bb.4
+    B %bb.5
+
+...