From 2949a6ae049a27a52053318ab29ab8d2775cc320 Mon Sep 17 00:00:00 2001
From: Michael Liao <michael.liao@intel.com>
Date: Mon, 19 Oct 2015 22:08:14 +0000
Subject: [PATCH] [InstCombine] Optimize icmp of inc/dec at RHS
Allow LLVM to optimize the sequence like the following:
%inc = add nsw i32 %i, 1
%cmp = icmp slt %n, %inc
into:
%cmp = icmp sle i32 %n, %i
The case is not handled previously due to the complexity of compuation of %n.
Hence, LLVM cannot swap operands of icmp accordingly.
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@250746 91177308-0d34-0410-b5e6-96231b3b80d8
---
.../InstCombine/InstCombineCompares.cpp | 20 ++++++++++
test/Transforms/InstCombine/icmp.ll | 40 +++++++++++++++++++
2 files changed, 60 insertions(+)
diff --git a/lib/Transforms/InstCombine/InstCombineCompares.cpp b/lib/Transforms/InstCombine/InstCombineCompares.cpp
index a333c3e18e5..e960b1bf05e 100644
--- a/lib/Transforms/InstCombine/InstCombineCompares.cpp
+++ b/lib/Transforms/InstCombine/InstCombineCompares.cpp
@@ -3426,6 +3426,26 @@ Instruction *InstCombiner::visitICmpInst(ICmpInst &I) {
match(B, m_One()))
return new ICmpInst(CmpInst::ICMP_SGE, A, Op1);
+ // icmp sgt X, (Y + -1) -> icmp sge X, Y
+ if (C && NoOp1WrapProblem && Pred == CmpInst::ICMP_SGT &&
+ match(D, m_AllOnes()))
+ return new ICmpInst(CmpInst::ICMP_SGE, Op0, C);
+
+ // icmp sle X, (Y + -1) -> icmp slt X, Y
+ if (C && NoOp1WrapProblem && Pred == CmpInst::ICMP_SLE &&
+ match(D, m_AllOnes()))
+ return new ICmpInst(CmpInst::ICMP_SLT, Op0, C);
+
+ // icmp sge X, (Y + 1) -> icmp sgt X, Y
+ if (C && NoOp1WrapProblem && Pred == CmpInst::ICMP_SGE &&
+ match(D, m_One()))
+ return new ICmpInst(CmpInst::ICMP_SGT, Op0, C);
+
+ // icmp slt X, (Y + 1) -> icmp sle X, Y
+ if (C && NoOp1WrapProblem && Pred == CmpInst::ICMP_SLT &&
+ match(D, m_One()))
+ return new ICmpInst(CmpInst::ICMP_SLE, Op0, C);
+
// if C1 has greater magnitude than C2:
// icmp (X + C1), (Y + C2) -> icmp (X + C3), Y
// s.t. C3 = C1 - C2
diff --git a/test/Transforms/InstCombine/icmp.ll b/test/Transforms/InstCombine/icmp.ll
index e351c81b15a..05f6678e354 100644
--- a/test/Transforms/InstCombine/icmp.ll
+++ b/test/Transforms/InstCombine/icmp.ll
@@ -1632,3 +1632,43 @@ entry:
%cmp580 = icmp ule i16 mul (i16 zext (i8 ptrtoint (i1 (i16)* @f10 to i8) to i16), i16 zext (i8 ptrtoint (i1 (i16)* @f10 to i8) to i16)), %p
ret i1 %cmp580
}
+
+; CHECK-LABEL: @cmp_sgt_rhs_dec
+; CHECK-NOT: sub
+; CHECK: icmp sge
+define i1 @cmp_sgt_rhs_dec(float %x, i32 %i) {
+ %conv = fptosi float %x to i32
+ %dec = sub nsw i32 %i, 1
+ %cmp = icmp sgt i32 %conv, %dec
+ ret i1 %cmp
+}
+
+; CHECK-LABEL: @cmp_sle_rhs_dec
+; CHECK-NOT: sub
+; CHECK: icmp slt
+define i1 @cmp_sle_rhs_dec(float %x, i32 %i) {
+ %conv = fptosi float %x to i32
+ %dec = sub nsw i32 %i, 1
+ %cmp = icmp sle i32 %conv, %dec
+ ret i1 %cmp
+}
+
+; CHECK-LABEL: @cmp_sge_rhs_inc
+; CHECK-NOT: add
+; CHECK: icmp sgt
+define i1 @cmp_sge_rhs_inc(float %x, i32 %i) {
+ %conv = fptosi float %x to i32
+ %inc = add nsw i32 %i, 1
+ %cmp = icmp sge i32 %conv, %inc
+ ret i1 %cmp
+}
+
+; CHECK-LABEL: @cmp_slt_rhs_inc
+; CHECK-NOT: add
+; CHECK: icmp sle
+define i1 @cmp_slt_rhs_inc(float %x, i32 %i) {
+ %conv = fptosi float %x to i32
+ %inc = add nsw i32 %i, 1
+ %cmp = icmp slt i32 %conv, %inc
+ ret i1 %cmp
+}
--
2.34.1