[PATCH] D157740: [WIP] [InstCombine] Fold icmp into phi beyond the same BB.

[Biplob Mishra via Phabricator via llvm-commits]

bipmis created this revision.
bipmis added reviewers: dmgreen, nikic, RKSimon.
bipmis added projects: LLVM, All.
Herald added a subscriber: StephenFan.
bipmis requested review of this revision.

Observing cases where folding a icmp into phi can be beneficial. Particularly if the above fold results in the icmp argument of type BinaryOperator, it may enable more folding. 
Need to understand if there is reason why the folding of icmp into phi happens within the same BB only.
Can this be done under additional checks.

Ran all tests. Looks Ok to me.


Repository:
  rG LLVM Github Monorepo

https://reviews.llvm.org/D157740

Files:
  llvm/lib/Transforms/InstCombine/InstCombineCompares.cpp
  llvm/test/Transforms/InstCombine/phi.ll


Index: llvm/test/Transforms/InstCombine/phi.ll
===================================================================
--- llvm/test/Transforms/InstCombine/phi.ll
+++ llvm/test/Transforms/InstCombine/phi.ll
@@ -2304,27 +2304,24 @@
 ; CHECK-NEXT:    [[INCDEC_PTR_I]] = getelementptr inbounds i8, ptr [[TEST_0_I]], i64 1
 ; CHECK-NEXT:    br i1 [[CMP1_NOT_I]], label [[WHILE_END_I:%.*]], label [[WHILE_COND_I]]
 ; CHECK:       while.end.i:
-; CHECK-NEXT:    [[SUB_PTR_LHS_CAST_I:%.*]] = ptrtoint ptr [[TEST_0_I]] to i64
-; CHECK-NEXT:    [[SUB_PTR_RHS_CAST_I:%.*]] = ptrtoint ptr [[VAL1]] to i64
-; CHECK-NEXT:    [[SUB_PTR_SUB_I:%.*]] = sub i64 [[SUB_PTR_LHS_CAST_I]], [[SUB_PTR_RHS_CAST_I]]
+; CHECK-NEXT:    [[TMP1:%.*]] = icmp ne ptr [[TEST_0_I]], [[VAL1]]
 ; CHECK-NEXT:    br label [[_Z3FOOPKC_EXIT]]
 ; CHECK:       _Z3fooPKc.exit:
-; CHECK-NEXT:    [[RETVAL_0_I:%.*]] = phi i64 [ [[SUB_PTR_SUB_I]], [[WHILE_END_I]] ], [ 0, [[ENTRY]] ]
+; CHECK-NEXT:    [[RETVAL_0_I:%.*]] = phi i1 [ [[TMP1]], [[WHILE_END_I]] ], [ false, [[ENTRY]] ]
 ; CHECK-NEXT:    [[CMP_I10:%.*]] = icmp eq ptr [[VAL2:%.*]], null
 ; CHECK-NEXT:    br i1 [[CMP_I10]], label [[_Z3FOOPKC_EXIT20:%.*]], label [[WHILE_COND_I11:%.*]]
 ; CHECK:       while.cond.i11:
 ; CHECK-NEXT:    [[TEST_0_I12:%.*]] = phi ptr [ [[INCDEC_PTR_I14:%.*]], [[WHILE_COND_I11]] ], [ [[VAL2]], [[_Z3FOOPKC_EXIT]] ]
-; CHECK-NEXT:    [[TMP1:%.*]] = load i8, ptr [[TEST_0_I12]], align 1
-; CHECK-NEXT:    [[CMP1_NOT_I13:%.*]] = icmp eq i8 [[TMP1]], 0
+; CHECK-NEXT:    [[TMP2:%.*]] = load i8, ptr [[TEST_0_I12]], align 1
+; CHECK-NEXT:    [[CMP1_NOT_I13:%.*]] = icmp eq i8 [[TMP2]], 0
 ; CHECK-NEXT:    [[INCDEC_PTR_I14]] = getelementptr inbounds i8, ptr [[TEST_0_I12]], i64 1
 ; CHECK-NEXT:    br i1 [[CMP1_NOT_I13]], label [[WHILE_END_I15:%.*]], label [[WHILE_COND_I11]]
 ; CHECK:       while.end.i15:
-; CHECK-NEXT:    [[TMP2:%.*]] = icmp ne ptr [[TEST_0_I12]], [[VAL2]]
+; CHECK-NEXT:    [[TMP3:%.*]] = icmp ne ptr [[TEST_0_I12]], [[VAL2]]
 ; CHECK-NEXT:    br label [[_Z3FOOPKC_EXIT20]]
 ; CHECK:       _Z3fooPKc.exit20:
-; CHECK-NEXT:    [[RETVAL_0_I19:%.*]] = phi i1 [ [[TMP2]], [[WHILE_END_I15]] ], [ false, [[_Z3FOOPKC_EXIT]] ]
-; CHECK-NEXT:    [[TOBOOL:%.*]] = icmp ne i64 [[RETVAL_0_I]], 0
-; CHECK-NEXT:    [[AND9:%.*]] = and i1 [[TOBOOL]], [[RETVAL_0_I19]]
+; CHECK-NEXT:    [[RETVAL_0_I19:%.*]] = phi i1 [ [[TMP3]], [[WHILE_END_I15]] ], [ false, [[_Z3FOOPKC_EXIT]] ]
+; CHECK-NEXT:    [[AND9:%.*]] = and i1 [[RETVAL_0_I]], [[RETVAL_0_I19]]
 ; CHECK-NEXT:    ret i1 [[AND9]]
 ;
 entry:
Index: llvm/lib/Transforms/InstCombine/InstCombineCompares.cpp
===================================================================
--- llvm/lib/Transforms/InstCombine/InstCombineCompares.cpp
+++ llvm/lib/Transforms/InstCombine/InstCombineCompares.cpp
@@ -3896,7 +3896,7 @@
     // Only fold icmp into the PHI if the phi and icmp are in the same
     // block.  If in the same block, we're encouraging jump threading.  If
     // not, we are just pessimizing the code by making an i1 phi.
-    if (LHSI->getParent() == I.getParent())
+    if (LHSI->getParent() == I.getParent() || isa<BinaryOperator>(LHSI->getOperand(0)))
       if (Instruction *NV = foldOpIntoPhi(I, cast<PHINode>(LHSI)))
         return NV;
     break;


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