[PATCH] D38242: [CGP] In optimizeMemoryInst handle select similarly to phi

[John Brawn via Phabricator via llvm-commits]

john.brawn created this revision.

This lets us optimize away selects that perform the same address computation in two different ways.


Repository:
  rL LLVM

https://reviews.llvm.org/D38242

Files:
  lib/CodeGen/CodeGenPrepare.cpp
  test/Transforms/CodeGenPrepare/X86/sink-addrmode.ll


Index: test/Transforms/CodeGenPrepare/X86/sink-addrmode.ll
===================================================================
--- test/Transforms/CodeGenPrepare/X86/sink-addrmode.ll
+++ test/Transforms/CodeGenPrepare/X86/sink-addrmode.ll
@@ -251,3 +251,20 @@
 exit:
   ret void
 }
+
+; Make sure we can eliminate a select when both arguments perform equivalent
+; address computation.
+define void @test10(i1 %cond, i64* %base) {
+; CHECK-LABEL: @test10
+; CHECK: getelementptr i8, {{.+}} 40
+; CHECK-NOT: select
+entry:
+  %gep1 = getelementptr inbounds i64, i64* %base, i64 5
+  %gep1.casted = bitcast i64* %gep1 to i32*
+  %base.casted = bitcast i64* %base to i32*
+  %gep2 = getelementptr inbounds i32, i32* %base.casted, i64 10
+  %casted.merged = select i1 %cond, i32* %gep1.casted, i32* %gep2
+  %v = load i32, i32* %casted.merged, align 4
+  call void @foo(i32 %v)
+  ret void
+}
Index: lib/CodeGen/CodeGenPrepare.cpp
===================================================================
--- lib/CodeGen/CodeGenPrepare.cpp
+++ lib/CodeGen/CodeGenPrepare.cpp
@@ -4389,9 +4389,9 @@
   SmallPtrSet<Value*, 16> Visited;
   worklist.push_back(Addr);
 
-  // Use a worklist to iteratively look through PHI nodes, and ensure that
-  // the addressing mode obtained from the non-PHI roots of the graph
-  // are equivalent.
+  // Use a worklist to iteratively look through PHI and select nodes, and
+  // ensure that the addressing mode obtained from the non-PHI/select roots of
+  // the graph are equivalent.
   bool AddrModeFound = false;
   bool PhiSeen = false;
   SmallVector<Instruction*, 16> AddrModeInsts;
@@ -4422,6 +4422,13 @@
       PhiSeen = true;
       continue;
     }
+    // Similar for select.
+    if (SelectInst *SI = dyn_cast<SelectInst>(V)) {
+      worklist.push_back(SI->getFalseValue());
+      worklist.push_back(SI->getTrueValue());
+      PhiSeen = true;
+      continue;
+    }
 
     // For non-PHIs, determine the addressing mode being computed.  Note that
     // the result may differ depending on what other uses our candidate


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