[PM] Schedule InstSimplify after late LICM run, to clean up LCSSA nodes.

manueljacob · manueljacob · commit a485984c0c88 · 2016-06-02T22:14:26.000Z
Summary: The module pass pipeline includes a late LICM run after loop unrolling. LCSSA is implicitly run as a pass dependency of LICM. However no cleanup pass was run after this, so the LCSSA nodes ended in the optimized output. Reviewers: hfinkel, mehdi_amini Subscribers: majnemer, bruno, mzolotukhin, mehdi_amini, llvm-commits Differential Revision: http://reviews.llvm.org/D20606 llvm-svn: 271602
diff --git a/llvm/lib/Transforms/IPO/PassManagerBuilder.cpp b/llvm/lib/Transforms/IPO/PassManagerBuilder.cpp
@@ -542,6 +542,9 @@ void PassManagerBuilder::populateModulePassManager(
     // outer loop. LICM pass can help to promote the runtime check out if the
     // checked value is loop invariant.
     MPM.add(createLICMPass());
+
+    // Get rid of LCSSA nodes.
+    MPM.add(createInstructionSimplifierPass());
   }
 
   // After vectorization and unrolling, assume intrinsics may tell us more
diff --git a/llvm/test/Other/cleanup-lcssa.ll b/llvm/test/Other/cleanup-lcssa.ll
@@ -0,0 +1,18 @@
+; RUN: opt -S -O3 < %s | FileCheck %s
+
+define i64 @test() {
+entry:
+  br label %loop
+
+loop:
+  %i = phi i64 [ 0, %entry ], [ %inc, %loop ]
+  %inc = add i64 %i, 1
+  %cond = tail call i1 @check()
+  br i1 %cond, label %loop, label %exit
+
+exit:
+  ; CHECK-NOT: lcssa
+  ret i64 %i
+}
+
+declare i1 @check()

Original file line number	Diff line number	Diff line change
`@@ -542,6 +542,9 @@ void PassManagerBuilder::populateModulePassManager(`
`542`	`542`	`// outer loop. LICM pass can help to promote the runtime check out if the`
`543`	`543`	`// checked value is loop invariant.`
`544`	`544`	`MPM.add(createLICMPass());`
	`545`	`+`
	`546`	`+ // Get rid of LCSSA nodes.`
	`547`	`+ MPM.add(createInstructionSimplifierPass());`
`545`	`548`	`}`
`546`	`549`
`547`	`550`	`// After vectorization and unrolling, assume intrinsics may tell us more`