From fbc2c8f2fbbb7fbc9a88ad64ac83de888d505d27 Mon Sep 17 00:00:00 2001
From: Sanjay Patel <spatel@rotateright.com>
Date: Thu, 10 Nov 2022 17:10:46 -0500
Subject: [PATCH] [InstSimplify] fold X +nnan Inf

If we exclude NaN (and therefore the opposite Inf),
anything plus Inf is Inf:
https://alive2.llvm.org/ce/z/og3dj9
---
 llvm/lib/Analysis/InstructionSimplify.cpp              | 18 +++++++++++-------
 .../InstSimplify/floating-point-arithmetic.ll          | 14 ++++++--------
 2 files changed, 17 insertions(+), 15 deletions(-)

diff --git a/llvm/lib/Analysis/InstructionSimplify.cpp b/llvm/lib/Analysis/InstructionSimplify.cpp
index c8b796a..b134234 100644
--- a/llvm/lib/Analysis/InstructionSimplify.cpp
+++ b/llvm/lib/Analysis/InstructionSimplify.cpp
@@ -5245,14 +5245,18 @@ simplifyFAddInst(Value *Op0, Value *Op1, FastMathFlags FMF,
   if (!isDefaultFPEnvironment(ExBehavior, Rounding))
     return nullptr;
 
-  // With nnan: -X + X --> 0.0 (and commuted variant)
-  // We don't have to explicitly exclude infinities (ninf): INF + -INF == NaN.
-  // Negative zeros are allowed because we always end up with positive zero:
-  // X = -0.0: (-0.0 - (-0.0)) + (-0.0) == ( 0.0) + (-0.0) == 0.0
-  // X = -0.0: ( 0.0 - (-0.0)) + (-0.0) == ( 0.0) + (-0.0) == 0.0
-  // X =  0.0: (-0.0 - ( 0.0)) + ( 0.0) == (-0.0) + ( 0.0) == 0.0
-  // X =  0.0: ( 0.0 - ( 0.0)) + ( 0.0) == ( 0.0) + ( 0.0) == 0.0
   if (FMF.noNaNs()) {
+    // With nnan: X + {+/-}Inf --> {+/-}Inf
+    if (match(Op1, m_Inf()))
+      return Op1;
+
+    // With nnan: -X + X --> 0.0 (and commuted variant)
+    // We don't have to explicitly exclude infinities (ninf): INF + -INF == NaN.
+    // Negative zeros are allowed because we always end up with positive zero:
+    // X = -0.0: (-0.0 - (-0.0)) + (-0.0) == ( 0.0) + (-0.0) == 0.0
+    // X = -0.0: ( 0.0 - (-0.0)) + (-0.0) == ( 0.0) + (-0.0) == 0.0
+    // X =  0.0: (-0.0 - ( 0.0)) + ( 0.0) == (-0.0) + ( 0.0) == 0.0
+    // X =  0.0: ( 0.0 - ( 0.0)) + ( 0.0) == ( 0.0) + ( 0.0) == 0.0
     if (match(Op0, m_FSub(m_AnyZeroFP(), m_Specific(Op1))) ||
         match(Op1, m_FSub(m_AnyZeroFP(), m_Specific(Op0))))
       return ConstantFP::getNullValue(Op0->getType());
diff --git a/llvm/test/Transforms/InstSimplify/floating-point-arithmetic.ll b/llvm/test/Transforms/InstSimplify/floating-point-arithmetic.ll
index 10a709e..14d179d 100644
--- a/llvm/test/Transforms/InstSimplify/floating-point-arithmetic.ll
+++ b/llvm/test/Transforms/InstSimplify/floating-point-arithmetic.ll
@@ -818,8 +818,7 @@ define float @maxnum_with_pos_one_op(float %a) {
 
 define double @fadd_nnan_inf_op0(double %x) {
 ; CHECK-LABEL: @fadd_nnan_inf_op0(
-; CHECK-NEXT:    [[R:%.*]] = fadd nnan double 0x7FF0000000000000, [[X:%.*]]
-; CHECK-NEXT:    ret double [[R]]
+; CHECK-NEXT:    ret double 0x7FF0000000000000
 ;
   %r = fadd nnan double 0x7ff0000000000000, %x
   ret double %r
@@ -827,8 +826,7 @@ define double @fadd_nnan_inf_op0(double %x) {
 
 define double @fadd_nnan_inf_op1(double %x) {
 ; CHECK-LABEL: @fadd_nnan_inf_op1(
-; CHECK-NEXT:    [[R:%.*]] = fadd nnan double [[X:%.*]], 0x7FF0000000000000
-; CHECK-NEXT:    ret double [[R]]
+; CHECK-NEXT:    ret double 0x7FF0000000000000
 ;
   %r = fadd nnan double %x, 0x7ff0000000000000
   ret double %r
@@ -836,8 +834,7 @@ define double @fadd_nnan_inf_op1(double %x) {
 
 define <2 x double> @fadd_nnan_neginf_op1(<2 x double> %x) {
 ; CHECK-LABEL: @fadd_nnan_neginf_op1(
-; CHECK-NEXT:    [[R:%.*]] = fadd nnan <2 x double> [[X:%.*]], <double 0xFFF0000000000000, double poison>
-; CHECK-NEXT:    ret <2 x double> [[R]]
+; CHECK-NEXT:    ret <2 x double> <double 0xFFF0000000000000, double poison>
 ;
   %r = fadd nnan <2 x double> %x, <double 0xfff0000000000000, double poison>
   ret <2 x double> %r
@@ -845,13 +842,14 @@ define <2 x double> @fadd_nnan_neginf_op1(<2 x double> %x) {
 
 define double @fadd_nnan_neginf_op0(double %x) {
 ; CHECK-LABEL: @fadd_nnan_neginf_op0(
-; CHECK-NEXT:    [[R:%.*]] = fadd nnan double 0xFFF0000000000000, [[X:%.*]]
-; CHECK-NEXT:    ret double [[R]]
+; CHECK-NEXT:    ret double 0xFFF0000000000000
 ;
   %r = fadd nnan double 0xfff0000000000000, %x
   ret double %r
 }
 
+; negative test - requires nnan
+
 define double @fadd_inf_op0(double %x) {
 ; CHECK-LABEL: @fadd_inf_op0(
 ; CHECK-NEXT:    [[R:%.*]] = fadd double 0x7FF0000000000000, [[X:%.*]]
-- 
2.7.4