From: Duncan Sands <baldrick@free.fr>
Date: Thu, 16 Dec 2010 09:40:54 +0000 (+0000)
Subject: Speculatively revert commit 121905 since it looks like it might have broken the
X-Git-Url: http://demsky.eecs.uci.edu/git/?a=commitdiff_plain;h=ebef48ea4b0d838d2e4f05024a517bf18b1cc110;p=oota-llvm.git

Speculatively revert commit 121905 since it looks like it might have broken the
dragonegg self-host buildbot.  Original commit message:

Add an InstCombine transform to recognize instances of manual overflow-safe addition
(performing the addition in a wider type and explicitly checking for overflow), and
fold them down to intrinsics.  This currently only supports signed-addition, but could
be generalized if someone works out the magic constant formulas for other operations.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@121965 91177308-0d34-0410-b5e6-96231b3b80d8
---

diff --git a/lib/Transforms/InstCombine/InstCombineCompares.cpp b/lib/Transforms/InstCombine/InstCombineCompares.cpp
index 0e711a1949c..d2841af8bc6 100644
--- a/lib/Transforms/InstCombine/InstCombineCompares.cpp
+++ b/lib/Transforms/InstCombine/InstCombineCompares.cpp
@@ -1657,71 +1657,6 @@ Instruction *InstCombiner::visitICmpInst(ICmpInst &I) {
   if (ConstantInt *CI = dyn_cast<ConstantInt>(Op1)) {
     Value *A = 0, *B = 0;
     
-    // Match the following pattern, which is a common idiom when writing
-    // overflow-safe integer arithmetic function.  The source performs an
-    // addition in wider type, and explicitly checks for overflow using
-    // comparisons against INT_MIN and INT_MAX.  Simplify this by using the
-    // sadd_with_overflow intrinsic.
-    // FIXME: This could probably be generalized to handle other overflow-safe
-    // operations if we worked out the formulas to compute the appropriate 
-    // magic constants.
-    // 
-    // INT64 : a, b, sum = a + b
-    // if sum < INT32_MIN || sum > INT_MAX then
-    //   ...
-    // else
-    //   ...
-    {
-    ConstantInt *CI2;
-    
-    // I = icmp ugt (add (add A B) CI2) CI
-    if (I.getPredicate() == ICmpInst::ICMP_UGT &&
-        match(Op0, m_Add(m_Add(m_Value(A), m_Value(B)),
-                   m_ConstantInt(CI2)))) {
-      const IntegerType *WideType = cast<IntegerType>(CI->getType());
-      unsigned WideWidth = WideType->getBitWidth();
-      unsigned NarrowWidth = WideWidth / 2;
-      const IntegerType *NarrowType =
-        IntegerType::get(CI->getContext(), NarrowWidth);
-      
-      // NarrowAllOnes and NarrowSignBit are the magic constants used to
-      // perform an overflow check in the wider type: 0x00..00FF..FF and
-      // 0x00..0010..00 respectively, where the highest set bit in each is
-      // what would be the sign bit in the narrower type.
-      ConstantInt *NarrowAllOnes = cast<ConstantInt>(ConstantInt::get(WideType,
-        APInt::getAllOnesValue(NarrowWidth).zext(WideWidth)));
-      APInt SignBit(WideWidth, 0);
-      SignBit.setBit(NarrowWidth-1);
-      ConstantInt *NarrowSignBit =
-       cast<ConstantInt>(ConstantInt::get(WideType, SignBit));
-      
-      if (CI == NarrowAllOnes && CI2 == NarrowSignBit) {
-        Module *M = I.getParent()->getParent()->getParent();
-        
-        const Type *IntrinsicType = NarrowType;
-        Value *F = Intrinsic::getDeclaration(M, Intrinsic::sadd_with_overflow,
-          &IntrinsicType, 1);
-        
-        // If the pattern matches, truncate the inputs to the narrower type and
-        // use the sadd_with_overflow intrinsic to efficiently compute both the
-        // result and the overflow bit.
-        Value *TruncA = Builder->CreateTrunc(A, NarrowType, A->getName());
-        Value *TruncB = Builder->CreateTrunc(B, NarrowType, B->getName());
-        CallInst *Call = Builder->CreateCall2(F, TruncA, TruncB);
-        Value *Add = Builder->CreateExtractValue(Call, 0);
-        Value *ZExt = Builder->CreateZExt(Add, WideType);
-        
-        // The inner add was the result of the narrow add, zero extended to the
-        // wider type.  Replace it with the result computed by the intrinsic.
-        Instruction *OrigAdd =
-          cast<Instruction>(cast<Instruction>(I.getOperand(0))->getOperand(0));
-        OrigAdd->replaceAllUsesWith(ZExt);
-        
-        return ExtractValueInst::Create(Call, 1);
-      }
-    }
-    }
-    
     // (icmp ne/eq (sub A B) 0) -> (icmp ne/eq A, B)
     if (I.isEquality() && CI->isZero() &&
         match(Op0, m_Sub(m_Value(A), m_Value(B)))) {
diff --git a/test/Transforms/InstCombine/overflow.ll b/test/Transforms/InstCombine/overflow.ll
deleted file mode 100644
index f3f8ca3d61d..00000000000
--- a/test/Transforms/InstCombine/overflow.ll
+++ /dev/null
@@ -1,27 +0,0 @@
-; RUN: opt -S -instcombine < %s | FileCheck %s
-; <rdar://problem/8558713>
-
-; CHECK: @test1
-define i32 @test1(i32 %a, i32 %b) nounwind ssp {
-entry:
-; CHECK-NOT: sext
-  %conv = sext i32 %a to i64
-  %conv2 = sext i32 %b to i64
-  %add = add nsw i64 %conv2, %conv
-  %add.off = add i64 %add, 2147483648
-; CHECK: llvm.sadd.with.overflow
-  %0 = icmp ugt i64 %add.off, 4294967295
-  br i1 %0, label %if.then, label %if.end
-
-if.then:
-  %call = tail call i32 (...)* @throwAnExceptionOrWhatever() nounwind
-  br label %if.end
-
-if.end:
-; CHECK-NOT: trunc
-  %conv9 = trunc i64 %add to i32
-; CHECK: ret i32
-  ret i32 %conv9
-}
-
-declare i32 @throwAnExceptionOrWhatever(...)