Work around a gcc 13 issue with signbit that made us not compute fmin of -0 properly (#5994)

2 files changed, 131 insertions, 4 deletions

diff --git a/src/wasm/literal.cpp b/src/wasm/literal.cpp
index 075028127..4bae54693 100644
--- a/src/wasm/literal.cpp
+++ b/src/wasm/literal.cpp
@@ -1526,8 +1526,12 @@ Literal Literal::min(const Literal& other) const {
       if (std::isnan(r)) {
         return standardizeNaN(Literal(r));
       }
+      // This code is written in a form that avoids a gcc 13 bug, see
+      // https://gcc.gnu.org/bugzilla/show_bug.cgi?id=111694
       if (l == r && l == 0) {
-        return Literal(std::signbit(l) ? l : r);
+        auto lSigned = std::signbit(l);
+        auto rSigned = std::signbit(r);
+        return Literal(lSigned || rSigned ? -0.0f : 0.0f);
       }
       return Literal(std::min(l, r));
     }
@@ -1540,7 +1544,9 @@ Literal Literal::min(const Literal& other) const {
         return standardizeNaN(Literal(r));
       }
       if (l == r && l == 0) {
-        return Literal(std::signbit(l) ? l : r);
+        auto lSigned = std::signbit(l);
+        auto rSigned = std::signbit(r);
+        return Literal(lSigned || rSigned ? -0.0 : 0.0);
       }
       return Literal(std::min(l, r));
     }
@@ -1560,7 +1566,9 @@ Literal Literal::max(const Literal& other) const {
         return standardizeNaN(Literal(r));
       }
       if (l == r && l == 0) {
-        return Literal(std::signbit(l) ? r : l);
+        auto lSigned = std::signbit(l);
+        auto rSigned = std::signbit(r);
+        return Literal(lSigned && rSigned ? -0.0f : 0.0f);
       }
       return Literal(std::max(l, r));
     }
@@ -1573,7 +1581,9 @@ Literal Literal::max(const Literal& other) const {
         return standardizeNaN(Literal(r));
       }
       if (l == r && l == 0) {
-        return Literal(std::signbit(l) ? r : l);
+        auto lSigned = std::signbit(l);
+        auto rSigned = std::signbit(r);
+        return Literal(lSigned && rSigned ? -0.0 : 0.0);
       }
       return Literal(std::max(l, r));
     }
diff --git a/test/lit/exec/negative-zero.wast b/test/lit/exec/negative-zero.wast
new file mode 100644
index 000000000..4a1e339ca
--- /dev/null
+++ b/test/lit/exec/negative-zero.wast
@@ -0,0 +1,117 @@
+;; NOTE: Assertions have been generated by update_lit_checks.py --output=fuzz-exec and should not be edited.
+
+;; RUN: wasm-opt %s -all --fuzz-exec -o /dev/null 2>&1 | filecheck %s
+
+(module
+ ;; CHECK:      [fuzz-exec] calling min1
+ ;; CHECK-NEXT: [fuzz-exec] note result: min1 => -0
+ (func "min1" (result f64)
+  ;; This should return -0.
+  (f64.min
+   (f64.const 0)
+   (f64.const -0)
+  )
+ )
+
+ ;; CHECK:      [fuzz-exec] calling min2
+ ;; CHECK-NEXT: [fuzz-exec] note result: min2 => -0
+ (func "min2" (result f64)
+  ;; Flipped arms; still -0.
+  (f64.min
+   (f64.const -0)
+   (f64.const 0)
+  )
+ )
+
+ ;; CHECK:      [fuzz-exec] calling min1-f32
+ ;; CHECK-NEXT: [fuzz-exec] note result: min1-f32 => -0
+ (func "min1-f32" (result f32)
+  ;; As above, but f32 and not f64
+  (f32.min
+   (f32.const 0)
+   (f32.const -0)
+  )
+ )
+
+ ;; CHECK:      [fuzz-exec] calling min2-f32
+ ;; CHECK-NEXT: [fuzz-exec] note result: min2-f32 => -0
+ (func "min2-f32" (result f32)
+  ;; Flipped arms; still -0.
+  (f32.min
+   (f32.const -0)
+   (f32.const 0)
+  )
+ )
+
+ ;; CHECK:      [fuzz-exec] calling max1
+ ;; CHECK-NEXT: [fuzz-exec] note result: max1 => 0
+ (func "max1" (result f64)
+  ;; This should return 0.
+  (f64.max
+   (f64.const 0)
+   (f64.const -0)
+  )
+ )
+
+ ;; CHECK:      [fuzz-exec] calling max2
+ ;; CHECK-NEXT: [fuzz-exec] note result: max2 => 0
+ (func "max2" (result f64)
+  ;; Flipped arms; still 0.
+  (f64.max
+   (f64.const -0)
+   (f64.const 0)
+  )
+ )
+
+ ;; CHECK:      [fuzz-exec] calling max1-f32
+ ;; CHECK-NEXT: [fuzz-exec] note result: max1-f32 => 0
+ (func "max1-f32" (result f32)
+  ;; As above, but f32 and not f64
+  (f32.max
+   (f32.const 0)
+   (f32.const -0)
+  )
+ )
+
+ ;; CHECK:      [fuzz-exec] calling max2-f32
+ ;; CHECK-NEXT: [fuzz-exec] note result: max2-f32 => 0
+ ;; CHECK-NEXT: warning: no passes specified, not doing any work
+ (func "max2-f32" (result f32)
+  ;; Flipped arms; still 0.
+  (f32.max
+   (f32.const -0)
+   (f32.const 0)
+  )
+ )
+)
+;; CHECK:      [fuzz-exec] calling min1
+;; CHECK-NEXT: [fuzz-exec] note result: min1 => -0
+
+;; CHECK:      [fuzz-exec] calling min2
+;; CHECK-NEXT: [fuzz-exec] note result: min2 => -0
+
+;; CHECK:      [fuzz-exec] calling min1-f32
+;; CHECK-NEXT: [fuzz-exec] note result: min1-f32 => -0
+
+;; CHECK:      [fuzz-exec] calling min2-f32
+;; CHECK-NEXT: [fuzz-exec] note result: min2-f32 => -0
+
+;; CHECK:      [fuzz-exec] calling max1
+;; CHECK-NEXT: [fuzz-exec] note result: max1 => 0
+
+;; CHECK:      [fuzz-exec] calling max2
+;; CHECK-NEXT: [fuzz-exec] note result: max2 => 0
+
+;; CHECK:      [fuzz-exec] calling max1-f32
+;; CHECK-NEXT: [fuzz-exec] note result: max1-f32 => 0
+
+;; CHECK:      [fuzz-exec] calling max2-f32
+;; CHECK-NEXT: [fuzz-exec] note result: max2-f32 => 0
+;; CHECK-NEXT: [fuzz-exec] comparing max1
+;; CHECK-NEXT: [fuzz-exec] comparing max1-f32
+;; CHECK-NEXT: [fuzz-exec] comparing max2
+;; CHECK-NEXT: [fuzz-exec] comparing max2-f32
+;; CHECK-NEXT: [fuzz-exec] comparing min1
+;; CHECK-NEXT: [fuzz-exec] comparing min1-f32
+;; CHECK-NEXT: [fuzz-exec] comparing min2
+;; CHECK-NEXT: [fuzz-exec] comparing min2-f32