On recent Intel u-arch's, folding loads into some unary SSE instructions can
be non-optimal. To be precise, we should avoid folding loads if the instructions
only update part of the destination register, and the non-updated part is not
needed. e.g. cvtss2sd, sqrtss. Unfolding the load from these instructions breaks
the partial register dependency and it can improve performance. e.g.
movss (%rdi), %xmm0
cvtss2sd %xmm0, %xmm0
instead of
cvtss2sd (%rdi), %xmm0
An alternative method to break dependency is to clear the register first. e.g.
xorps %xmm0, %xmm0
cvtss2sd (%rdi), %xmm0
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@91672 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/lib/Target/X86/X86Subtarget.cpp b/lib/Target/X86/X86Subtarget.cpp
index 75cdbad..4db3fdb 100644
--- a/lib/Target/X86/X86Subtarget.cpp
+++ b/lib/Target/X86/X86Subtarget.cpp
@@ -266,6 +266,7 @@
unsigned Model = 0;
DetectFamilyModel(EAX, Family, Model);
IsBTMemSlow = IsAMD || (Family == 6 && Model >= 13);
+ BreakSSEDep = IsIntel;
GetCpuIDAndInfo(0x80000001, &EAX, &EBX, &ECX, &EDX);
HasX86_64 = (EDX >> 29) & 0x1;
@@ -286,6 +287,7 @@
, HasFMA3(false)
, HasFMA4(false)
, IsBTMemSlow(false)
+ , BreakSSEDep(false)
, DarwinVers(0)
, stackAlignment(8)
// FIXME: this is a known good value for Yonah. How about others?