[PATCH] D98080: [gvn] Handle simply phi equivalence cases

[Philip Reames via Phabricator via llvm-commits]

This revision was landed with ongoing or failed builds.
This revision was automatically updated to reflect the committed changes.
Closed by commit rG5db2735af91b: [gvn] Handle simply phi equivalence cases (authored by reames).

Repository:
  rG LLVM Github Monorepo

CHANGES SINCE LAST ACTION
  https://reviews.llvm.org/D98080/new/

https://reviews.llvm.org/D98080

Files:
  llvm/lib/Transforms/Scalar/GVN.cpp
  llvm/test/Transforms/GVN/phi.ll


Index: llvm/test/Transforms/GVN/phi.ll
===================================================================
--- llvm/test/Transforms/GVN/phi.ll
+++ llvm/test/Transforms/GVN/phi.ll
@@ -11,9 +11,7 @@
 ; CHECK-NEXT:    br label [[MERGE]]
 ; CHECK:       merge:
 ; CHECK-NEXT:    [[PHI1:%.*]] = phi i64 [ [[A:%.*]], [[TAKEN]] ], [ [[B:%.*]], [[UNTAKEN]] ]
-; CHECK-NEXT:    [[PHI2:%.*]] = phi i64 [ [[A]], [[TAKEN]] ], [ [[B]], [[UNTAKEN]] ]
-; CHECK-NEXT:    [[RET:%.*]] = sub i64 [[PHI1]], [[PHI2]]
-; CHECK-NEXT:    ret i64 [[RET]]
+; CHECK-NEXT:    ret i64 0
 ;
   br i1 %c, label %taken, label %untaken
 taken:
@@ -69,9 +67,7 @@
 ; CHECK-NEXT:    br label [[MERGE]]
 ; CHECK:       merge:
 ; CHECK-NEXT:    [[PHI1:%.*]] = phi i64 [ [[ADD1]], [[TAKEN]] ], [ [[B:%.*]], [[UNTAKEN]] ]
-; CHECK-NEXT:    [[PHI2:%.*]] = phi i64 [ [[ADD1]], [[TAKEN]] ], [ [[B]], [[UNTAKEN]] ]
-; CHECK-NEXT:    [[RET:%.*]] = sub i64 [[PHI1]], [[PHI2]]
-; CHECK-NEXT:    ret i64 [[RET]]
+; CHECK-NEXT:    ret i64 0
 ;
   br i1 %c, label %taken, label %untaken
 taken:
@@ -96,19 +92,15 @@
 ; CHECK-NEXT:    br label [[MERGE]]
 ; CHECK:       merge:
 ; CHECK-NEXT:    [[PHI1:%.*]] = phi i64 [ [[A:%.*]], [[TAKEN]] ], [ [[B:%.*]], [[UNTAKEN]] ]
-; CHECK-NEXT:    [[PHI2:%.*]] = phi i64 [ [[A]], [[TAKEN]] ], [ [[B]], [[UNTAKEN]] ]
 ; CHECK-NEXT:    br i1 [[C]], label [[TAKEN2:%.*]], label [[UNTAKEN2:%.*]]
 ; CHECK:       taken2:
 ; CHECK-NEXT:    [[ADD1:%.*]] = add i64 [[PHI1]], 5
-; CHECK-NEXT:    [[ADD2:%.*]] = add i64 [[PHI2]], 5
 ; CHECK-NEXT:    br label [[MERGE2:%.*]]
 ; CHECK:       untaken2:
 ; CHECK-NEXT:    br label [[MERGE2]]
 ; CHECK:       merge2:
-; CHECK-NEXT:    [[PHI3:%.*]] = phi i64 [ [[ADD1]], [[TAKEN2]] ], [ [[PHI2]], [[UNTAKEN2]] ]
-; CHECK-NEXT:    [[PHI4:%.*]] = phi i64 [ [[ADD2]], [[TAKEN2]] ], [ [[PHI2]], [[UNTAKEN2]] ]
-; CHECK-NEXT:    [[RET:%.*]] = sub i64 [[PHI4]], [[PHI3]]
-; CHECK-NEXT:    ret i64 [[RET]]
+; CHECK-NEXT:    [[PHI3:%.*]] = phi i64 [ [[ADD1]], [[TAKEN2]] ], [ [[PHI1]], [[UNTAKEN2]] ]
+; CHECK-NEXT:    ret i64 0
 ;
   br i1 %c, label %taken, label %untaken
 taken:
Index: llvm/lib/Transforms/Scalar/GVN.cpp
===================================================================
--- llvm/lib/Transforms/Scalar/GVN.cpp
+++ llvm/lib/Transforms/Scalar/GVN.cpp
@@ -2372,6 +2372,12 @@
   ReplaceOperandsWithMap.clear();
   bool ChangedFunction = false;
 
+  // Since we may not have visited the input blocks of the phis, we can't
+  // use our normal hash approach for phis.  Instead, simply look for
+  // obvious duplicates.  The first pass of GVN will tend to create
+  // identical phis, and the second or later passes can eliminate them.
+  ChangedFunction |= EliminateDuplicatePHINodes(BB);
+
   for (BasicBlock::iterator BI = BB->begin(), BE = BB->end();
        BI != BE;) {
     if (!ReplaceOperandsWithMap.empty())


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