[PATCH] D26096: [ValueTracking] recognize obfuscated variants of umin/umax

[Sanjay Patel via llvm-commits]

spatel updated this revision to Diff 76312.
spatel added a comment.

Patch updated - rebase after https://reviews.llvm.org/rL285499 , but no difference in intent/functionality:

1. Insert the unsigned min/max pattern matching block next to the updated signed min/max block.
2. Changed name of test file since we have signed and unsigned tests now.


https://reviews.llvm.org/D26096

Files:
  lib/Analysis/ValueTracking.cpp
  test/CodeGen/X86/vec_minmax_match.ll


Index: test/CodeGen/X86/vec_minmax_match.ll
===================================================================
--- test/CodeGen/X86/vec_minmax_match.ll
+++ test/CodeGen/X86/vec_minmax_match.ll
@@ -60,15 +60,10 @@
   ret <4 x i32> %sel
 }
 
-; FIXME: These are unsigned min/max ops.
-
 define <4 x i32> @umax_vec1(<4 x i32> %x) {
 ; CHECK-LABEL: umax_vec1:
 ; CHECK:       # BB#0:
-; CHECK-NEXT:    vpxor %xmm1, %xmm1, %xmm1
-; CHECK-NEXT:    vpcmpgtd %xmm0, %xmm1, %xmm1
-; CHECK-NEXT:    vmovaps {{.*#+}} xmm2 = [2147483647,2147483647,2147483647,2147483647]
-; CHECK-NEXT:    vblendvps %xmm1, %xmm0, %xmm2, %xmm0
+; CHECK-NEXT:    vpmaxud {{.*}}(%rip), %xmm0, %xmm0
 ; CHECK-NEXT:    retq
 ;
   %cmp = icmp slt <4 x i32> %x, zeroinitializer
@@ -79,9 +74,7 @@
 define <4 x i32> @umax_vec2(<4 x i32> %x) {
 ; CHECK-LABEL: umax_vec2:
 ; CHECK:       # BB#0:
-; CHECK-NEXT:    vpcmpeqd %xmm1, %xmm1, %xmm1
-; CHECK-NEXT:    vpcmpgtd %xmm1, %xmm0, %xmm1
-; CHECK-NEXT:    vblendvps %xmm1, {{.*}}(%rip), %xmm0, %xmm0
+; CHECK-NEXT:    vpmaxud {{.*}}(%rip), %xmm0, %xmm0
 ; CHECK-NEXT:    retq
 ;
   %cmp = icmp sgt <4 x i32> %x, <i32 -1, i32 -1, i32 -1, i32 -1>
@@ -92,9 +85,7 @@
 define <4 x i32> @umin_vec1(<4 x i32> %x) {
 ; CHECK-LABEL: umin_vec1:
 ; CHECK:       # BB#0:
-; CHECK-NEXT:    vpxor %xmm1, %xmm1, %xmm1
-; CHECK-NEXT:    vpcmpgtd %xmm0, %xmm1, %xmm1
-; CHECK-NEXT:    vblendvps %xmm1, {{.*}}(%rip), %xmm0, %xmm0
+; CHECK-NEXT:    vpminud {{.*}}(%rip), %xmm0, %xmm0
 ; CHECK-NEXT:    retq
 ;
   %cmp = icmp slt <4 x i32> %x, zeroinitializer
@@ -105,10 +96,7 @@
 define <4 x i32> @umin_vec2(<4 x i32> %x) {
 ; CHECK-LABEL: umin_vec2:
 ; CHECK:       # BB#0:
-; CHECK-NEXT:    vpcmpeqd %xmm1, %xmm1, %xmm1
-; CHECK-NEXT:    vpcmpgtd %xmm1, %xmm0, %xmm1
-; CHECK-NEXT:    vmovaps {{.*#+}} xmm2 = [2147483648,2147483648,2147483648,2147483648]
-; CHECK-NEXT:    vblendvps %xmm1, %xmm0, %xmm2, %xmm0
+; CHECK-NEXT:    vpminud {{.*}}(%rip), %xmm0, %xmm0
 ; CHECK-NEXT:    retq
 ;
   %cmp = icmp sgt <4 x i32> %x, <i32 -1, i32 -1, i32 -1, i32 -1>
Index: lib/Analysis/ValueTracking.cpp
===================================================================
--- lib/Analysis/ValueTracking.cpp
+++ lib/Analysis/ValueTracking.cpp
@@ -3969,9 +3969,33 @@
       }
     }
 
+    // An unsigned min/max can be written with a signed compare.
+    const APInt *C2;
+    if ((CmpLHS == TrueVal && match(FalseVal, m_APInt(C2))) ||
+        (CmpLHS == FalseVal && match(TrueVal, m_APInt(C2)))) {
+      // Is the sign bit set?
+      // (X <s 0) ? X : MAXVAL ==> (X >u MAXVAL) ? X : MAXVAL ==> UMAX
+      // (X <s 0) ? MAXVAL : X ==> (X >u MAXVAL) ? MAXVAL : X ==> UMIN
+      if (Pred == CmpInst::ICMP_SLT && *C1 == 0 && C2->isMaxSignedValue()) {
+        LHS = TrueVal;
+        RHS = FalseVal;
+        return {CmpLHS == TrueVal ? SPF_UMAX : SPF_UMIN, SPNB_NA, false};
+      }
+
+      // Is the sign bit clear?
+      // (X >s -1) ? MINVAL : X ==> (X <u MINVAL) ? MINVAL : X ==> UMAX
+      // (X >s -1) ? X : MINVAL ==> (X <u MINVAL) ? X : MINVAL ==> UMIN
+      if (Pred == CmpInst::ICMP_SGT && C1->isAllOnesValue() &&
+          C2->isMinSignedValue()) {
+        LHS = TrueVal;
+        RHS = FalseVal;
+        return {CmpLHS == FalseVal ? SPF_UMAX : SPF_UMIN, SPNB_NA, false};
+      }
+    }
+
+    // Look through 'not' ops to find disguised signed min/max.
     // (X >s C) ? ~X : ~C ==> (~X <s ~C) ? ~X : ~C ==> SMIN(~X, ~C)
     // (X <s C) ? ~X : ~C ==> (~X >s ~C) ? ~X : ~C ==> SMAX(~X, ~C)
-    const APInt *C2;
     if (match(TrueVal, m_Not(m_Specific(CmpLHS))) &&
         match(FalseVal, m_APInt(C2)) && ~(*C1) == *C2 &&
         (Pred == CmpInst::ICMP_SGT || Pred == CmpInst::ICMP_SLT)) {


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