Emit a more efficient magic number multiplication for exact sdivs.
We have to do this in DAGBuilder instead of DAGCombiner, because the exact bit is lost after building.
struct foo { char x[24]; };
long bar(struct foo *a, struct foo *b) { return a-b; }
is now compiled into
movl 4(%esp), %eax
subl 8(%esp), %eax
sarl $3, %eax
imull $-1431655765, %eax, %eax
instead of
movl 4(%esp), %eax
subl 8(%esp), %eax
movl $715827883, %ecx
imull %ecx
movl %edx, %eax
shrl $31, %eax
sarl $2, %edx
addl %eax, %edx
movl %edx, %eax
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@134695 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/lib/CodeGen/SelectionDAG/SelectionDAGBuilder.h b/lib/CodeGen/SelectionDAG/SelectionDAGBuilder.h
index a1ca891..a0884eb 100644
--- a/lib/CodeGen/SelectionDAG/SelectionDAGBuilder.h
+++ b/lib/CodeGen/SelectionDAG/SelectionDAGBuilder.h
@@ -467,7 +467,7 @@
void visitSRem(const User &I) { visitBinary(I, ISD::SREM); }
void visitFRem(const User &I) { visitBinary(I, ISD::FREM); }
void visitUDiv(const User &I) { visitBinary(I, ISD::UDIV); }
- void visitSDiv(const User &I) { visitBinary(I, ISD::SDIV); }
+ void visitSDiv(const User &I);
void visitFDiv(const User &I) { visitBinary(I, ISD::FDIV); }
void visitAnd (const User &I) { visitBinary(I, ISD::AND); }
void visitOr (const User &I) { visitBinary(I, ISD::OR); }