[ValueTracking] recognize variations of 'clamp' to improve codegen (PR31693)
By enhancing value tracking, we allow an existing min/max canonicalization to
kick in and improve codegen for several targets that have min/max instructions.
Unfortunately, recognizing min/max in value tracking may cause us to hit
a hack in InstCombiner::visitICmpInst() more often:
http://lists.llvm.org/pipermail/llvm-dev/2017-January/109340.html
...but I'm hoping we can remove that soon.
Correctness proofs based on Alive:
Name: smaxmin
Pre: C1 < C2
%cmp2 = icmp slt i8 %x, C2
%min = select i1 %cmp2, i8 %x, i8 C2
%cmp3 = icmp slt i8 %x, C1
%r = select i1 %cmp3, i8 C1, i8 %min
=>
%cmp2 = icmp slt i8 %x, C2
%min = select i1 %cmp2, i8 %x, i8 C2
%cmp1 = icmp sgt i8 %min, C1
%r = select i1 %cmp1, i8 %min, i8 C1
Name: sminmax
Pre: C1 > C2
%cmp2 = icmp sgt i8 %x, C2
%max = select i1 %cmp2, i8 %x, i8 C2
%cmp3 = icmp sgt i8 %x, C1
%r = select i1 %cmp3, i8 C1, i8 %max
=>
%cmp2 = icmp sgt i8 %x, C2
%max = select i1 %cmp2, i8 %x, i8 C2
%cmp1 = icmp slt i8 %max, C1
%r = select i1 %cmp1, i8 %max, i8 C1
----------------------------------------
Optimization: smaxmin
Done: 1
Optimization is correct!
----------------------------------------
Optimization: sminmax
Done: 1
Optimization is correct!
Name: umaxmin
Pre: C1 u< C2
%cmp2 = icmp ult i8 %x, C2
%min = select i1 %cmp2, i8 %x, i8 C2
%cmp3 = icmp ult i8 %x, C1
%r = select i1 %cmp3, i8 C1, i8 %min
=>
%cmp2 = icmp ult i8 %x, C2
%min = select i1 %cmp2, i8 %x, i8 C2
%cmp1 = icmp ugt i8 %min, C1
%r = select i1 %cmp1, i8 %min, i8 C1
Name: uminmax
Pre: C1 u> C2
%cmp2 = icmp ugt i8 %x, C2
%max = select i1 %cmp2, i8 %x, i8 C2
%cmp3 = icmp ugt i8 %x, C1
%r = select i1 %cmp3, i8 C1, i8 %max
=>
%cmp2 = icmp ugt i8 %x, C2
%max = select i1 %cmp2, i8 %x, i8 C2
%cmp1 = icmp ult i8 %max, C1
%r = select i1 %cmp1, i8 %max, i8 C1
----------------------------------------
Optimization: umaxmin
Done: 1
Optimization is correct!
----------------------------------------
Optimization: uminmax
Done: 1
Optimization is correct!
llvm-svn: 292660
diff --git a/llvm/lib/Analysis/ValueTracking.cpp b/llvm/lib/Analysis/ValueTracking.cpp
index 0053623..4f18cc8 100644
--- a/llvm/lib/Analysis/ValueTracking.cpp
+++ b/llvm/lib/Analysis/ValueTracking.cpp
@@ -3918,6 +3918,45 @@
Value *CmpLHS, Value *CmpRHS,
Value *TrueVal, Value *FalseVal,
Value *&LHS, Value *&RHS) {
+ // Recognize variations of:
+ // CLAMP(v,l,h) ==> ((v) < (l) ? (l) : ((v) > (h) ? (h) : (v)))
+ const APInt *C1;
+ if (CmpRHS == TrueVal && match(CmpRHS, m_APInt(C1))) {
+ const APInt *C2;
+
+ // (X <s C1) ? C1 : SMIN(X, C2) ==> SMAX(SMIN(X, C2), C1)
+ if (match(FalseVal, m_SMin(m_Specific(CmpLHS), m_APInt(C2))) &&
+ C1->slt(*C2) && Pred == CmpInst::ICMP_SLT) {
+ LHS = TrueVal;
+ RHS = FalseVal;
+ return {SPF_SMAX, SPNB_NA, false};
+ }
+
+ // (X >s C1) ? C1 : SMAX(X, C2) ==> SMIN(SMAX(X, C2), C1)
+ if (match(FalseVal, m_SMax(m_Specific(CmpLHS), m_APInt(C2))) &&
+ C1->sgt(*C2) && Pred == CmpInst::ICMP_SGT) {
+ LHS = TrueVal;
+ RHS = FalseVal;
+ return {SPF_SMIN, SPNB_NA, false};
+ }
+
+ // (X <u C1) ? C1 : UMIN(X, C2) ==> UMAX(UMIN(X, C2), C1)
+ if (match(FalseVal, m_UMin(m_Specific(CmpLHS), m_APInt(C2))) &&
+ C1->ult(*C2) && Pred == CmpInst::ICMP_ULT) {
+ LHS = TrueVal;
+ RHS = FalseVal;
+ return {SPF_UMAX, SPNB_NA, false};
+ }
+
+ // (X >u C1) ? C1 : UMAX(X, C2) ==> UMIN(UMAX(X, C2), C1)
+ if (match(FalseVal, m_UMax(m_Specific(CmpLHS), m_APInt(C2))) &&
+ C1->ugt(*C2) && Pred == CmpInst::ICMP_UGT) {
+ LHS = TrueVal;
+ RHS = FalseVal;
+ return {SPF_UMIN, SPNB_NA, false};
+ }
+ }
+
if (Pred != CmpInst::ICMP_SGT && Pred != CmpInst::ICMP_SLT)
return {SPF_UNKNOWN, SPNB_NA, false};
@@ -3941,7 +3980,6 @@
return {Pred == CmpInst::ICMP_SGT ? SPF_SMAX : SPF_SMIN, SPNB_NA, false};
}
- const APInt *C1;
if (!match(CmpRHS, m_APInt(C1)))
return {SPF_UNKNOWN, SPNB_NA, false};