[llvm] r204912 - InstCombine: merge constants in both operands of icmp.

[Erik Verbruggen]

Author: erikjv
Date: Thu Mar 27 06:16:05 2014
New Revision: 204912

URL: http://llvm.org/viewvc/llvm-project?rev=204912&view=rev
Log:
InstCombine: merge constants in both operands of icmp.

Transform:
    icmp X+Cst2, Cst
into:
    icmp X, Cst-Cst2
when Cst-Cst2 does not overflow, and the add has nsw.

Modified:
    llvm/trunk/lib/Target/README.txt
    llvm/trunk/lib/Transforms/InstCombine/InstCombineCompares.cpp
    llvm/trunk/test/Transforms/InstCombine/icmp.ll

Modified: llvm/trunk/lib/Target/README.txt
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Target/README.txt?rev=204912&r1=204911&r2=204912&view=diff
==============================================================================
--- llvm/trunk/lib/Target/README.txt (original)
+++ llvm/trunk/lib/Target/README.txt Thu Mar 27 06:16:05 2014
@@ -930,18 +930,6 @@ optimized with "clang -emit-llvm-bc | op
 
 //===---------------------------------------------------------------------===//
 
-int g(int x) { return (x - 10) < 0; }
-Should combine to "x <= 9" (the sub has nsw).  Currently not
-optimized with "clang -emit-llvm-bc | opt -std-compile-opts".
-
-//===---------------------------------------------------------------------===//
-
-int g(int x) { return (x + 10) < 0; }
-Should combine to "x < -10" (the add has nsw).  Currently not
-optimized with "clang -emit-llvm-bc | opt -std-compile-opts".
-
-//===---------------------------------------------------------------------===//
-
 int f(int i, int j) { return i < j + 1; }
 int g(int i, int j) { return j > i - 1; }
 Should combine to "i <= j" (the add/sub has nsw).  Currently not

Modified: llvm/trunk/lib/Transforms/InstCombine/InstCombineCompares.cpp
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Transforms/InstCombine/InstCombineCompares.cpp?rev=204912&r1=204911&r2=204912&view=diff
==============================================================================
--- llvm/trunk/lib/Transforms/InstCombine/InstCombineCompares.cpp (original)
+++ llvm/trunk/lib/Transforms/InstCombine/InstCombineCompares.cpp Thu Mar 27 06:16:05 2014
@@ -3008,6 +3008,19 @@ Instruction *InstCombiner::visitICmpInst
     // icmp X, X+Cst
     if (match(Op1, m_Add(m_Value(X), m_ConstantInt(Cst))) && Op0 == X)
       return FoldICmpAddOpCst(I, X, Cst, I.getSwappedPredicate());
+
+    ConstantInt *Cst2;
+    if (match(Op1, m_ConstantInt(Cst)) &&
+        match(Op0, m_Add(m_Value(X), m_ConstantInt(Cst2))) &&
+        cast<BinaryOperator>(Op0)->hasNoSignedWrap()) {
+      // icmp X+Cst2, Cst --> icmp X, Cst-Cst2
+      // iff Cst-Cst2 does not overflow
+      bool Overflow;
+      APInt NewCst = Cst->getValue().ssub_ov(Cst2->getValue(), Overflow);
+      if (!Overflow)
+        return new ICmpInst(I.getPredicate(), X,
+                            ConstantInt::get(Cst->getType(), NewCst));
+    }
   }
   return Changed ? &I : 0;
 }

Modified: llvm/trunk/test/Transforms/InstCombine/icmp.ll
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/test/Transforms/InstCombine/icmp.ll?rev=204912&r1=204911&r2=204912&view=diff
==============================================================================
--- llvm/trunk/test/Transforms/InstCombine/icmp.ll (original)
+++ llvm/trunk/test/Transforms/InstCombine/icmp.ll Thu Mar 27 06:16:05 2014
@@ -1356,3 +1356,56 @@ define i1 @icmp_ashr_ashr_ne(i32 %a, i32
  %z = icmp ne i32 %x, %y
  ret i1 %z
 }
+
+; CHECK-LABEL: icmp_add_const_const1
+; CHECK: %cmp = icmp slt i32 %x, -10
+; CHECK-NOT: %add = add nsw i32 %x, 10
+define i32 @icmp_add_const_const1(i32 %x) nounwind ssp uwtable {
+entry:
+  %add = add nsw i32 %x, 10
+  %cmp = icmp slt i32 %add, 0
+  %conv = zext i1 %cmp to i32
+  ret i32 %conv
+}
+
+; CHECK-LABEL: icmp_add_const_const2
+; CHECK: %cmp = icmp slt i32 %x, -10
+; CHECK-NOT: %add = add nsw i32 %x, 10
+define i32 @icmp_add_const_const2(i32 %x) nounwind ssp uwtable {
+entry:
+  %add = add nsw i32 10, %x
+  %cmp = icmp sgt i32 0, %add
+  %conv = zext i1 %cmp to i32
+  ret i32 %conv
+}
+
+; CHECK-LABEL: icmp_add_const_const3
+; CHECK: %cmp = icmp slt i32 %x, 20
+; CHECK-NOT: %sub = add nsw i32 %x, -10
+define i32 @icmp_add_const_const3(i32 %x) nounwind ssp uwtable {
+entry:
+  %add = add nsw i32 -10, %x
+  %cmp = icmp sgt i32 10, %add
+  %conv = zext i1 %cmp to i32
+  ret i32 %conv
+}
+
+; CHECK-LABEL: icmp_add_const_intmin
+; CHECK: %cmp = icmp ne i32 %x, 2147483638
+define i32 @icmp_add_const_intmin(i32 %x) nounwind ssp uwtable {
+entry:
+  %add = add nsw i32 %x, 10
+  %cmp = icmp sgt i32 %add, -2147483648
+  %conv = zext i1 %cmp to i32
+  ret i32 %conv
+}
+
+; CHECK-LABEL: icmp_add_const_intmax
+; CHECK: %cmp = icmp ne i32 %x, 2147483637
+define i32 @icmp_add_const_intmax(i32 %x) nounwind ssp uwtable {
+entry:
+  %add = add nsw i32 %x, 10
+  %cmp = icmp slt i32 %add, 2147483647
+  %conv = zext i1 %cmp to i32
+  ret i32 %conv
+}