[PATCH] D79217: Process gep (select ptr1, ptr2) in SROA

[Stanislav Mekhanoshin via Phabricator via llvm-commits]

rampitec created this revision.
rampitec added a reviewer: arsenm.
Herald added subscribers: hiraditya, wdng.
Herald added a project: LLVM.

https://reviews.llvm.org/D79217

Files:
  llvm/lib/Transforms/Scalar/SROA.cpp
  llvm/test/Transforms/SROA/select-gep.ll


Index: llvm/test/Transforms/SROA/select-gep.ll
===================================================================
--- /dev/null
+++ llvm/test/Transforms/SROA/select-gep.ll
@@ -0,0 +1,35 @@
+; NOTE: Assertions have been autogenerated by utils/update_test_checks.py
+; RUN: opt -S -sroa < %s | FileCheck %s
+
+%pair = type { i32, i32 }
+
+define i32 @test_sroa_select_gep(i1 %cond) {
+; CHECK-LABEL: @test_sroa_select_gep(
+; CHECK-NEXT:  bb:
+; CHECK-NEXT:    [[LOAD_SROA_SPECULATED:%.*]] = select i1 [[COND:%.*]], i32 undef, i32 undef
+; CHECK-NEXT:    ret i32 [[LOAD_SROA_SPECULATED]]
+;
+bb:
+  %a = alloca %pair, align 4
+  %b = alloca %pair, align 4
+  %select = select i1 %cond, %pair* %a, %pair* %b
+  %gep = getelementptr inbounds %pair, %pair* %select, i32 0, i32 1
+  %load = load i32, i32* %gep, align 4
+  ret i32 %load
+}
+
+define i32 @test_sroa_select_gep_undef(i1 %cond) {
+; CHECK-LABEL: @test_sroa_select_gep_undef(
+; CHECK-NEXT:  bb:
+; CHECK-NEXT:    [[A_SROA_0:%.*]] = alloca i32
+; CHECK-NEXT:    [[SELECT_SROA_SEL:%.*]] = select i1 [[COND:%.*]], i32* [[A_SROA_0]], i32* undef
+; CHECK-NEXT:    [[LOAD:%.*]] = load i32, i32* [[SELECT_SROA_SEL]], align 4
+; CHECK-NEXT:    ret i32 [[LOAD]]
+;
+bb:
+  %a = alloca %pair, align 4
+  %select = select i1 %cond, %pair* %a, %pair* undef
+  %gep = getelementptr inbounds %pair, %pair* %select, i32 0, i32 1
+  %load = load i32, i32* %gep, align 4
+  ret i32 %load
+}
Index: llvm/lib/Transforms/Scalar/SROA.cpp
===================================================================
--- llvm/lib/Transforms/Scalar/SROA.cpp
+++ llvm/lib/Transforms/Scalar/SROA.cpp
@@ -3464,6 +3464,46 @@
   }
 
   bool visitGetElementPtrInst(GetElementPtrInst &GEPI) {
+    // Fold gep (select cond, ptr1, ptr2) => select cond, gep(ptr1), gep(ptr2)
+    if (SelectInst *Sel = dyn_cast<SelectInst>(GEPI.getPointerOperand())) {
+      LLVM_DEBUG(dbgs() << "  Rewriting gep(select) -> select(gep):"
+                        << "\n    original: " << *Sel
+                        << "\n              " << GEPI);
+      IRBuilderTy Builder(&GEPI);
+      SmallVector<Value *, 4> Index(GEPI.idx_begin(), GEPI.idx_end());
+      bool IsInBounds = GEPI.isInBounds();
+
+      Value *True = Sel->getTrueValue();
+      Value *NTrue =
+          IsInBounds
+              ? Builder.CreateInBoundsGEP(True, Index,
+                                          True->getName() + ".sroa.gep")
+              : Builder.CreateGEP(True, Index, True->getName() + ".sroa.gep");
+
+      Value *False = Sel->getFalseValue();
+
+      Value *NFalse =
+          IsInBounds
+              ? Builder.CreateInBoundsGEP(False, Index,
+                                          False->getName() + ".sroa.gep")
+              : Builder.CreateGEP(False, Index, False->getName() + ".sroa.gep");
+
+      Value *NSel = Builder.CreateSelect(Sel->getCondition(), NTrue, NFalse,
+                                         Sel->getName() + ".sroa.sel");
+      GEPI.replaceAllUsesWith(NSel);
+      GEPI.eraseFromParent();
+
+      LLVM_DEBUG(dbgs() << "\n          to: " << *NTrue
+                        << "\n              " << *NFalse
+                        << "\n              " << *NSel << '\n');
+
+      if (isa<Instruction>(NTrue))
+        visit(cast<Instruction>(NTrue));
+      if (isa<Instruction>(NFalse))
+        visit(cast<Instruction>(NFalse));
+      return true;
+    }
+
     enqueueUsers(GEPI);
     return false;
   }


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