From a5fda70c1316cffa8af0d7d835fcd421f498b4ff Mon Sep 17 00:00:00 2001
From: Hal Finkel <hfinkel@anl.gov>
Date: Sat, 4 Oct 2014 21:27:06 +0000
Subject: [PATCH] [InstCombine] Remove redundant @llvm.assume intrinsics

For any @llvm.assume intrinsic, if there is another which dominates it and uses
the same condition, then it is redundant and can be removed. While this does
not alter the semantics of the @llvm.assume intrinsics, it makes subsequent
handling more efficient (and the resulting IR easier to read).

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@219067 91177308-0d34-0410-b5e6-96231b3b80d8
---
 .../InstCombine/InstCombineCalls.cpp          | 17 ++++++
 .../InstCombine/assume-redundant.ll           | 55 +++++++++++++++++++
 2 files changed, 72 insertions(+)
 create mode 100644 test/Transforms/InstCombine/assume-redundant.ll

diff --git a/lib/Transforms/InstCombine/InstCombineCalls.cpp b/lib/Transforms/InstCombine/InstCombineCalls.cpp
index 30fc3c93383..27a64d8bcde 100644
--- a/lib/Transforms/InstCombine/InstCombineCalls.cpp
+++ b/lib/Transforms/InstCombine/InstCombineCalls.cpp
@@ -16,6 +16,7 @@
 #include "llvm/Analysis/MemoryBuiltins.h"
 #include "llvm/IR/CallSite.h"
 #include "llvm/IR/DataLayout.h"
+#include "llvm/IR/Dominators.h"
 #include "llvm/IR/PatternMatch.h"
 #include "llvm/Transforms/Utils/BuildLibCalls.h"
 #include "llvm/Transforms/Utils/Local.h"
@@ -1016,6 +1017,22 @@ Instruction *InstCombiner::visitCallInst(CallInst &CI) {
                           II->getName());
       return EraseInstFromFunction(*II);
     }
+
+    // If there is a dominating assume with the same condition as this one,
+    // then this one is redundant, and should be removed.
+    if (DT) {
+      for (User *U : IIOperand->users()) {
+        Instruction *User = dyn_cast<Instruction>(U);
+        if (!User || User == II)
+          continue;
+
+        if (match(User,
+                  m_Intrinsic<Intrinsic::assume>(m_Specific(IIOperand))) &&
+            DT->dominates(User, II))
+          return EraseInstFromFunction(*II);
+      }
+    }
+
     break;
   }
   }
diff --git a/test/Transforms/InstCombine/assume-redundant.ll b/test/Transforms/InstCombine/assume-redundant.ll
new file mode 100644
index 00000000000..81fe0945949
--- /dev/null
+++ b/test/Transforms/InstCombine/assume-redundant.ll
@@ -0,0 +1,55 @@
+; RUN: opt -domtree -instcombine -loops -S < %s | FileCheck %s
+; Note: The -loops above can be anything that requires the domtree, and is
+; necessary to work around a pass-manager bug.
+
+target datalayout = "e-m:e-i64:64-f80:128-n8:16:32:64-S128"
+target triple = "x86_64-unknown-linux-gnu"
+
+%struct.s = type { double* }
+
+; Function Attrs: nounwind uwtable
+define void @_Z3fooR1s(%struct.s* nocapture readonly dereferenceable(8) %x) #0 {
+
+; CHECK-LABEL: @_Z3fooR1s
+; CHECK: call void @llvm.assume
+; CHECK-NOT: call void @llvm.assume
+
+entry:
+  %a = getelementptr inbounds %struct.s* %x, i64 0, i32 0
+  %0 = load double** %a, align 8
+  %ptrint = ptrtoint double* %0 to i64
+  %maskedptr = and i64 %ptrint, 31
+  %maskcond = icmp eq i64 %maskedptr, 0
+  br label %for.body
+
+for.body:                                         ; preds = %for.body, %entry
+  %indvars.iv = phi i64 [ 0, %entry ], [ %indvars.iv.next.1, %for.body ]
+  tail call void @llvm.assume(i1 %maskcond)
+  %arrayidx = getelementptr inbounds double* %0, i64 %indvars.iv
+  %1 = load double* %arrayidx, align 16
+  %add = fadd double %1, 1.000000e+00
+  tail call void @llvm.assume(i1 %maskcond)
+  %mul = fmul double %add, 2.000000e+00
+  store double %mul, double* %arrayidx, align 16
+  %indvars.iv.next = add nuw nsw i64 %indvars.iv, 1
+  tail call void @llvm.assume(i1 %maskcond)
+  %arrayidx.1 = getelementptr inbounds double* %0, i64 %indvars.iv.next
+  %2 = load double* %arrayidx.1, align 8
+  %add.1 = fadd double %2, 1.000000e+00
+  tail call void @llvm.assume(i1 %maskcond)
+  %mul.1 = fmul double %add.1, 2.000000e+00
+  store double %mul.1, double* %arrayidx.1, align 8
+  %indvars.iv.next.1 = add nuw nsw i64 %indvars.iv.next, 1
+  %exitcond.1 = icmp eq i64 %indvars.iv.next, 1599
+  br i1 %exitcond.1, label %for.end, label %for.body
+
+for.end:                                          ; preds = %for.body
+  ret void
+}
+
+; Function Attrs: nounwind
+declare void @llvm.assume(i1) #1
+
+attributes #0 = { nounwind uwtable }
+attributes #1 = { nounwind }
+
-- 
2.34.1