[PATCH] D45378: [InstCombine] Propagate null values from conditions to other basic blocks

[Dávid Bolvanský via Phabricator via llvm-commits]

xbolva00 updated this revision to Diff 141426.
xbolva00 marked 3 inline comments as done.

https://reviews.llvm.org/D45378

Files:
  lib/Transforms/InstCombine/InstructionCombining.cpp
  test/Transforms/InstCombine/cond-return-null.ll


Index: test/Transforms/InstCombine/cond-return-null.ll
===================================================================
--- /dev/null
+++ test/Transforms/InstCombine/cond-return-null.ll
@@ -0,0 +1,41 @@
+; RUN: opt < %s -instcombine -S | FileCheck %s
+
+ at .str = private unnamed_addr constant [1 x i8] zeroinitializer, align 1
+
+define i8* @propagate_null(i8* %ptr) #0 {
+; CHECK-LABEL: @propagate_null(
+; CHECK-NEXT:  entry:
+; CHECK-NEXT:    [[TOBOOL:%.*]] = icmp eq i8* [[PTR:%.*]], null
+; CHECK-NEXT:    br i1 [[TOBOOL]], label [[IF_THEN:%.*]], label [[IF_END:%.*]]
+; CHECK:       if.then:
+; CHECK-NEXT:    br label [[RETURN:%.*]]
+; CHECK:       if.end:
+; CHECK-NEXT:    [[PUTCHAR:%.*]] = call i32 @putchar(i32 10)
+; CHECK-NEXT:    br label [[RETURN]]
+; CHECK:       return:
+; CHECK-NEXT:    [[STOREMERGE:%.*]] = phi i8* [ [[PTR]], [[IF_END]] ], [ null, [[IF_THEN]] ]
+; CHECK-NEXT:    ret i8* [[STOREMERGE]]
+;
+
+
+
+entry:
+  %retval = alloca i8*, align 4
+  %tobool = icmp ne i8* %ptr, null
+  br i1 %tobool, label %if.end, label %if.then
+
+if.then:                                          ; preds = %entry
+  store i8* null, i8** %retval, align 4
+  br label %return
+
+if.end:                                           ; preds = %entry
+  %call = call i32 @puts(i8* getelementptr inbounds ([1 x i8], [1 x i8]* @.str, i32 0, i32 0))
+  store i8* %ptr, i8** %retval, align 4
+  br label %return
+
+return:                                           ; preds = %if.end, %if.then
+  %0 = load i8*, i8** %retval, align 4
+  ret i8* %0
+}
+
+declare i32 @puts(i8*) #1
Index: lib/Transforms/InstCombine/InstructionCombining.cpp
===================================================================
--- lib/Transforms/InstCombine/InstructionCombining.cpp
+++ lib/Transforms/InstCombine/InstructionCombining.cpp
@@ -2392,6 +2392,32 @@
     return &BI;
   }
 
+  // Propagate null op from cmp to next basic blocks
+  if (match(&BI, m_Br(m_OneUse(m_Cmp(Pred, m_Value(), m_Zero())), TrueDest,
+                      FalseDest)) &&
+      isCanonicalPredicate(Pred)) {
+    auto Cmp = dyn_cast<CmpInst>(BI.getOperand(0));
+    auto NullOp = Cmp->getOperand(0);
+    auto B = TrueDest;
+    bool NullOpReplaced = false;
+    while (B) {
+      for (Instruction &I : *B) {
+        for (unsigned i = 0; i < I.getNumOperands(); ++i) {
+          auto Arg = I.getOperand(i);
+          if (match(Arg, m_Zero()) && NullOp->getType() == Arg->getType()) {
+            I.setOperand(i, NullOp);
+            NullOpReplaced |= true;
+          }
+        }
+      }
+
+      B = B->getNextNode();
+    }
+
+    if (NullOpReplaced)
+      return &BI;
+  }
+
   return nullptr;
 }
 


-------------- next part --------------
A non-text attachment was scrubbed...
Name: D45378.141426.patch
Type: text/x-patch
Size: 2679 bytes
Desc: not available
URL: <http://lists.llvm.org/pipermail/llvm-commits/attachments/20180406/ccc2a6be/attachment.bin>