[PATCH] [tree-optimization] Optimize max/min pattern with comparison

[Eugene Rozenfeld <Eugene.Rozenfeld@microsoft.com>]

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Make the following simplifications:
    X <= MAX(X, Y) -> true
    X > MAX(X, Y) -> false
    X >= MIN(X, Y) -> true
    X < MIN(X, Y) -> false
    
This fixes PR96708.
    
Tested on x86_64-pc-linux-gnu.

bool f(int a, int b)
{
    int tmp = (a < b) ? b : a;
    return tmp >= a;
}

Code without the patch:

vmovd  xmm0,edi
vmovd  xmm1,esi
vpmaxsd xmm0,xmm0,xmm1
vmovd  eax,xmm0
cmp    eax,edi
setge  al
ret    

Code with the patch:

mov    eax,0x1
ret

Eugene

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From f6391c197b670b516238ac7707512c1358336520 Mon Sep 17 00:00:00 2001
From: Eugene Rozenfeld <erozen@microsoft.com>
Date: Sat, 21 Nov 2020 01:08:50 -0800
Subject: [PATCH] Optimize max pattern with comparison

Make the following simplifications:
X <= MAX(X, Y) -> true
X > MAX(X, Y) -> false
X >= MIN(X, Y) -> true
X < MIN(X, Y) -> false

This fixes PR96708.

gcc/
* match.pd : New patterns.
---
 gcc/match.pd | 10 ++++++++++
 1 file changed, 10 insertions(+)

diff --git a/gcc/match.pd b/gcc/match.pd
index cbb4bf0b32d..75237741946 100644
--- a/gcc/match.pd
+++ b/gcc/match.pd
@@ -2851,6 +2851,16 @@ DEFINE_INT_AND_FLOAT_ROUND_FN (RINT)
   (cmp (minmax @0 INTEGER_CST@1) INTEGER_CST@2)
   (comb (cmp @0 @2) (cmp @1 @2))))
 
+/* X <= MAX(X, Y) -> true
+   X > MAX(X, Y) -> false 
+   X >= MIN(X, Y) -> true
+   X < MIN(X, Y) -> false */
+(for minmax (min     min     max     max     )
+     cmp    (ge      lt      le      gt      )
+ (simplify
+  (cmp @0 (minmax:c @0 @1))
+  { constant_boolean_node (cmp == GE_EXPR || cmp == LE_EXPR, type); } ))
+
 /* Undo fancy way of writing max/min or other ?: expressions,
    like a - ((a - b) & -(a < b)), in this case into (a < b) ? b : a.
    People normally use ?: and that is what we actually try to optimize.  */
-- 
2.17.1