[ELF] Fix precedence of ? when there are 2 or more operators on the left hand side

For 1 != 1 <= 1 ? 1 : 2, the current code incorrectly considers that ?
has a higher precedence than != (minPrec).

Also, add a test for right associativity.

Author: MaskRay

lld/ELF/ScriptParser.cpp

@@ -645,6 +645,7 @@ static int precedence(StringRef op) {
       .Case("|", 4)
       .Case("&&", 3)
       .Case("||", 2)
+      .Case("?", 1)
       .Default(-1);
 }
 
@@ -1128,11 +1129,11 @@ Expr ScriptParser::combine(StringRef op, Expr l, Expr r) {
 Expr ScriptParser::readExpr1(Expr lhs, int minPrec) {
   while (!atEOF() && !errorCount()) {
     // Read an operator and an expression.
-    if (consume("?"))
-      return readTernary(lhs);
     StringRef op1 = peek();
     if (precedence(op1) < minPrec)
       break;
+    if (consume("?"))
+      return readTernary(lhs);
     skip();
     Expr rhs = readPrimary();
 

lld/test/ELF/linkerscript/operators.test

@@ -13,14 +13,14 @@ SECTIONS {
   nospace = 1+2*6/3;
   braces = 1 + (2 + 3) * 4;
   and = 0xbb & 0xee;
-  ternary1 = 1 ? 1 : 2;
+  ternary1 = 1 ? 2 : 3 ? 4 : 5;
   ternary2 = 0 ? 1 : 2;
   less = 1 < 0 ? 1 : 2;
   lesseq = 1 <= 1 ? 1 : 2;
   greater = 0 > 1 ? 1 : 2;
   greatereq = 1 >= 1 ? 1 : 2;
   eq = 1 == 1 ? 1 : 2;
-  neq = (1 != 1 <= 1) ? 1 : 2;
+  neq = 1 != 1 <= 1 ? 1 : 2;
   plusassign = 1;
   plusassign += 2;
   unary = -1 + 3;
@@ -64,7 +64,7 @@ SECTIONS {
 # CHECK-NEXT: 00000000000005 A nospace
 # CHECK-NEXT: 00000000000015 A braces
 # CHECK-NEXT: 000000000000aa A and
-# CHECK-NEXT: 00000000000001 A ternary1
+# CHECK-NEXT: 00000000000002 A ternary1
 # CHECK-NEXT: 00000000000002 A ternary2
 # CHECK-NEXT: 00000000000002 A less
 # CHECK-NEXT: 00000000000001 A lesseq