[PATCH] D21769: [InstCombine] shrink type of sdiv if dividend is sexted and constant divisor is small enough (PR28153)
Sanjay Patel via llvm-commits
llvm-commits at lists.llvm.org
Mon Jun 27 15:34:17 PDT 2016
This revision was automatically updated to reflect the committed changes.
Closed by commit rL273951: [InstCombine] shrink type of sdiv if dividend is sexted and constant divisor… (authored by spatel).
Changed prior to commit:
http://reviews.llvm.org/D21769?vs=62013&id=62027#toc
Repository:
rL LLVM
http://reviews.llvm.org/D21769
Files:
llvm/trunk/lib/Transforms/InstCombine/InstCombineMulDivRem.cpp
llvm/trunk/test/Transforms/InstCombine/div.ll
Index: llvm/trunk/lib/Transforms/InstCombine/InstCombineMulDivRem.cpp
===================================================================
--- llvm/trunk/lib/Transforms/InstCombine/InstCombineMulDivRem.cpp
+++ llvm/trunk/lib/Transforms/InstCombine/InstCombineMulDivRem.cpp
@@ -1150,6 +1150,23 @@
Value *ShAmt = ConstantInt::get(Op1->getType(), Op1C->exactLogBase2());
return BinaryOperator::CreateExactAShr(Op0, ShAmt, I.getName());
}
+
+ // If the dividend is sign-extended and the constant divisor is small enough
+ // to fit in the source type, shrink the division to the narrower type:
+ // (sext X) sdiv C --> sext (X sdiv C)
+ Value *Op0Src;
+ if (match(Op0, m_OneUse(m_SExt(m_Value(Op0Src)))) &&
+ Op0Src->getType()->getScalarSizeInBits() >= Op1C->getMinSignedBits()) {
+
+ // In the general case, we need to make sure that the dividend is not the
+ // minimum signed value because dividing that by -1 is UB. But here, we
+ // know that the -1 divisor case is already handled above.
+
+ Constant *NarrowDivisor =
+ ConstantExpr::getTrunc(cast<Constant>(Op1), Op0Src->getType());
+ Value *NarrowOp = Builder->CreateSDiv(Op0Src, NarrowDivisor);
+ return new SExtInst(NarrowOp, Op0->getType());
+ }
}
if (Constant *RHS = dyn_cast<Constant>(Op1)) {
Index: llvm/trunk/test/Transforms/InstCombine/div.ll
===================================================================
--- llvm/trunk/test/Transforms/InstCombine/div.ll
+++ llvm/trunk/test/Transforms/InstCombine/div.ll
@@ -409,13 +409,12 @@
ret i32 %div
}
-; FIXME:
; We can perform the division in the smaller type.
define i32 @shrink(i8 %x) {
; CHECK-LABEL: @shrink(
-; CHECK-NEXT: [[CONV:%.*]] = sext i8 %x to i32
-; CHECK-NEXT: [[DIV:%.*]] = sdiv i32 [[CONV]], 127
+; CHECK-NEXT: [[TMP1:%.*]] = sdiv i8 %x, 127
+; CHECK-NEXT: [[DIV:%.*]] = sext i8 [[TMP1]] to i32
; CHECK-NEXT: ret i32 [[DIV]]
;
%conv = sext i8 %x to i32
@@ -427,8 +426,8 @@
define i32 @zap(i8 %x) {
; CHECK-LABEL: @zap(
-; CHECK-NEXT: [[CONV:%.*]] = sext i8 %x to i32
-; CHECK-NEXT: [[DIV:%.*]] = sdiv i32 [[CONV]], -128
+; CHECK-NEXT: [[TMP1:%.*]] = icmp eq i8 %x, -128
+; CHECK-NEXT: [[DIV:%.*]] = zext i1 [[TMP1]] to i32
; CHECK-NEXT: ret i32 [[DIV]]
;
%conv = sext i8 %x to i32
@@ -440,8 +439,8 @@
define <3 x i32> @shrink_vec(<3 x i8> %x) {
; CHECK-LABEL: @shrink_vec(
-; CHECK-NEXT: [[CONV:%.*]] = sext <3 x i8> %x to <3 x i32>
-; CHECK-NEXT: [[DIV:%.*]] = sdiv <3 x i32> [[CONV]], <i32 127, i32 127, i32 127>
+; CHECK-NEXT: [[TMP1:%.*]] = sdiv <3 x i8> %x, <i8 127, i8 127, i8 127>
+; CHECK-NEXT: [[DIV:%.*]] = sext <3 x i8> [[TMP1]] to <3 x i32>
; CHECK-NEXT: ret <3 x i32> [[DIV]]
;
%conv = sext <3 x i8> %x to <3 x i32>
@@ -451,8 +450,8 @@
define <2 x i32> @zap_vec(<2 x i8> %x) {
; CHECK-LABEL: @zap_vec(
-; CHECK-NEXT: [[CONV:%.*]] = sext <2 x i8> %x to <2 x i32>
-; CHECK-NEXT: [[DIV:%.*]] = sdiv <2 x i32> [[CONV]], <i32 -128, i32 -128>
+; CHECK-NEXT: [[TMP1:%.*]] = icmp eq <2 x i8> %x, <i8 -128, i8 -128>
+; CHECK-NEXT: [[DIV:%.*]] = zext <2 x i1> [[TMP1]] to <2 x i32>
; CHECK-NEXT: ret <2 x i32> [[DIV]]
;
%conv = sext <2 x i8> %x to <2 x i32>
@@ -484,3 +483,16 @@
ret i32 %div
}
+; 17 bits are needed to represent 65535 as a signed value, so this shouldn't fold.
+
+define i32 @shrink_no3(i16 %x) {
+; CHECK-LABEL: @shrink_no3(
+; CHECK-NEXT: [[CONV:%.*]] = sext i16 %x to i32
+; CHECK-NEXT: [[DIV:%.*]] = sdiv i32 [[CONV]], 65535
+; CHECK-NEXT: ret i32 [[DIV]]
+;
+ %conv = sext i16 %x to i32
+ %div = sdiv i32 %conv, 65535
+ ret i32 %div
+}
+
-------------- next part --------------
A non-text attachment was scrubbed...
Name: D21769.62027.patch
Type: text/x-patch
Size: 3701 bytes
Desc: not available
URL: <http://lists.llvm.org/pipermail/llvm-commits/attachments/20160627/521d2d2b/attachment.bin>
More information about the llvm-commits
mailing list