[llvm] r301880 - [InstSimplify] Handle selects of GEPs with 0 offset

George Burgess IV via llvm-commits llvm-commits at lists.llvm.org
Mon May 1 16:12:08 PDT 2017


Author: gbiv
Date: Mon May  1 18:12:08 2017
New Revision: 301880

URL: http://llvm.org/viewvc/llvm-project?rev=301880&view=rev
Log:
[InstSimplify] Handle selects of GEPs with 0 offset

In particular (since it wouldn't fit nicely in the summary):
(select (icmp eq V 0) P (getelementptr P V)) -> (getelementptr P V)

Differential Revision: https://reviews.llvm.org/D31435

Modified:
    llvm/trunk/lib/Analysis/InstructionSimplify.cpp
    llvm/trunk/test/Transforms/InstSimplify/select.ll

Modified: llvm/trunk/lib/Analysis/InstructionSimplify.cpp
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Analysis/InstructionSimplify.cpp?rev=301880&r1=301879&r2=301880&view=diff
==============================================================================
--- llvm/trunk/lib/Analysis/InstructionSimplify.cpp (original)
+++ llvm/trunk/lib/Analysis/InstructionSimplify.cpp Mon May  1 18:12:08 2017
@@ -62,6 +62,8 @@ static Value *SimplifyOrInst(Value *, Va
 static Value *SimplifyXorInst(Value *, Value *, const SimplifyQuery &, unsigned);
 static Value *SimplifyCastInst(unsigned, Value *, Type *,
                                const SimplifyQuery &, unsigned);
+static Value *SimplifyGEPInst(Type *, ArrayRef<Value *>, const SimplifyQuery &,
+                              unsigned);
 
 /// For a boolean type or a vector of boolean type, return false or a vector
 /// with every element false.
@@ -3491,6 +3493,17 @@ static const Value *SimplifyWithOpReplac
     }
   }
 
+  // Same for GEPs.
+  if (auto *GEP = dyn_cast<GetElementPtrInst>(I)) {
+    if (MaxRecurse) {
+      SmallVector<Value *, 8> NewOps(GEP->getNumOperands());
+      transform(GEP->operands(), NewOps.begin(),
+                [&](Value *V) { return V == Op ? RepOp : V; });
+      return SimplifyGEPInst(GEP->getSourceElementType(), NewOps, Q,
+                             MaxRecurse - 1);
+    }
+  }
+
   // TODO: We could hand off more cases to instsimplify here.
 
   // If all operands are constant after substituting Op for RepOp then we can

Modified: llvm/trunk/test/Transforms/InstSimplify/select.ll
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/test/Transforms/InstSimplify/select.ll?rev=301880&r1=301879&r2=301880&view=diff
==============================================================================
--- llvm/trunk/test/Transforms/InstSimplify/select.ll (original)
+++ llvm/trunk/test/Transforms/InstSimplify/select.ll Mon May  1 18:12:08 2017
@@ -431,3 +431,22 @@ define i8 @do_not_assume_sel_cond(i1 %co
   ret i8 %sel
 }
 
+define i32* @select_icmp_eq_0_gep_operand(i32* %base, i64 %n) {
+; CHECK-LABEL: @select_icmp_eq_0_gep_operand(
+; CHECK-NEXT: [[GEP:%.*]] = getelementptr
+; CHECK-NEXT: ret i32* [[GEP]]
+  %cond = icmp eq i64 %n, 0
+  %gep = getelementptr i32, i32* %base, i64 %n
+  %r = select i1 %cond, i32* %base, i32* %gep
+  ret i32* %r
+}
+
+define i32* @select_icmp_ne_0_gep_operand(i32* %base, i64 %n) {
+; CHECK-LABEL: @select_icmp_ne_0_gep_operand(
+; CHECK-NEXT: [[GEP:%.*]] = getelementptr
+; CHECK-NEXT: ret i32* [[GEP]]
+  %cond = icmp ne i64 %n, 0
+  %gep = getelementptr i32, i32* %base, i64 %n
+  %r = select i1 %cond, i32* %gep, i32* %base
+  ret i32* %r
+}




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